Close
0%
0%

Clockwork germanium

A retro version of Yet Another (Discrete) Clock, with vintage parts

Similar projects worth following
Imagine you're in the ealy 20th century, with the old technology but with all the knowledge of today. What would you do ?

* Resistors and capacitors are well known and industrially manufactured
* Piezo-electricity was studied by Pierre & Jacques Curie in 1880. In the 1920s, Pierce nailed oscillators and in 1927, the first quartz-synched clock was built by Warren Marrison and J.W. Horton at Bell Labs.
* Point-contact diodes are from the 1900s too
* The LED effect was first observed in a point-contact diode in 1907. Actual production began in the 1960s.
* The bipolar transistor was discovered in 1947 (more or less simultaneously at Bell Labs and in France by Germans)

Let's say we're in the 1950s and gotten seed funding. Making a clock would be a logical application despite the higher parts cost compared to radios. Logic gates are more tolerant to leakage, low gain and fab variations. Indeed, early computers were built out of low-grade transistors!

This is the "neovintage" version of #Yet Another (Discrete) Clock using original old parts as much as possible "for research purpose".

I (@Yann Guidon / YGDES) receive help from two contributors who have more experience with Germanium than me: @Alexander Shabarshin and @jaromir.sukuba. This is invaluable to decypher russian parts and cyrillic data sheets or circuits, thank you guys ! Alexander writes some of the logs, and he also started his own germanium clock project using circuits we develop here.


Expect power consumption to be higher than the MOSFET version, but fortunately, the invention of the transfer resistor is saving us the insane amounts needed to power the heating elements of vacuum tubes. Relays don't need high voltages either ;-)

Some design constraints

  • old/vintage parts wherever possible and whenever available
  • 4.5V power supply from alkaline batteries (so power consumption should be kept low and supply varies between 4V and 5V))
  • PNP Germanium transistors is the major type, though NPN is really required at some places
  • Low frequency Crystal oscillator as discrete clock source (I got down to 2500 cycles/s !)

Structure

The clock is made of a similar design as the #Yet Another (Discrete) Clock but the technology is a bit different so one single module will not fit all. We mostly need

  • Divide-by-two cell for the frequency divider (similar to )
  • Flip-flop cell for the Johnson counters (2, 3 and 5 stages). No schematic defined/found yet but it might be adapted from the 4-T of this 50 years old circuit:

The Johnson counters directly drive the LEDs:

This diagram must be corrected because it works well for MOSFETs but Ge BJTs behave differently, the previous sentence means "there is no 7-segments decoder".

Clock:

The chosen clock source is a 18KHz quartz resonator in a glass tube. Others, slower, are considered, depending on availability. Total: 39 FlipFlops (the initial estimate).


Logs:

1. 1st approach
2. Testing Germanium transistors
3. Crystal oscillator
4. Germanium diodes
5. 2nd approach
6. Testing Germanium transistors (2nd part)
7. Crystal Oscillator (Germanium Edition)
8. Triggering Germanium
9. Vintage transistor book
10. Got Quartz !
11. Reverse-engineering vintage quartz resonators
12. It just works
13. More ingredients to cook germanium
14. PCB received
15. New inventory
16. Easier frequency division
17. Another interesting BJT DFF circuit
18. More bistables
19. Even more bistables !
20. Even more bistables: plot twist !
21. More bistables...
22. I don't know why it works
23. D-FF without metastability
24. First shift register
25. Germanium is not for ever...
26. Towards a smaller shift register
27. Pulser-sequencer
28. Reduction by mirroring
29. Germanium lemonade
30. More inspiration
31. More Germanium lemonade, OC70 edition
32. Working bistable at last !
33. Funny clock preamp
34. Inside OC70
35. Clock preamp 3T
.

  • 400 × OC70 Vintage Germanium PNP transistor

  • Clock preamp 3T

    Yann Guidon / YGDES08/25/2023 at 22:28 9 comments

    This circuit seems to work well in simulation, provided you let the first input stage settle for a while, as it charges the 10nF coupling cap.

    We have seen the first stage in a previous log so no need to repeat it : it uses the coupling cap as a reservoir too, so it takes a while for the bias to get "right" through the 10M resistor. On its own, it can amplify quite a bit, at least in amplitude. But the output drops as soon as some load is tied.

    Then an emitter follower "buffers" the output. It acts almost as a Darlington pair with the 3rd but there are impedance issues so a RC network makes the junction.

    Then a final stage does the saturated voltage amplification to get cleaner edges and a decent rise/fall time.

    All transistors are set as hFE=20. Notice the various resistors : 470K, 47K then 4.7K, reducing impedance by 10x at each step.

    The 10M pull-up has a strange behaviour in the simulation, as it raises the 3rd transistor's base above 5V, sometimes 6.5V depending on the capacitor and other factors. 47pF is "mostly harmless" but really helps with the output rise times.

    The output signal drops when a load is tied, and I want to have even lower output impedance to drive 2 clock signals.

    Of course the same usual limitations apply !

    • The transistor of the simulation is not a Germanium type
    • Leakage is not taken into account
    • Baker capacitances are not considered either

    So there will be quite a lot of differences but the simulation helped me understand the role of each part's value.

  • Inside OC70

    Yann Guidon / YGDES08/23/2023 at 21:35 3 comments

    I have a few OC70 (or so it seems, as there is no marking).

    But it's not easy to look inside the glass casing, because it is filled with a silicon grease mixed with opaque alumina powder... to prevent people from scratching the cellulose black paint and use it as a phototransistor. This had to be done with a OCP71, the very same thing but sold 3× the price, because the sikicone grease is clear.

    This is shown in the pictures below :

    The left shows the stock OC70 with some black paint scratched, and the right is the OCP71. We can only infer that the insides are identical. So let's zoom inside the OCP71 :

    It's an "alloy" transistor where the doped germanium chip is tied to the base (the large electrode), and the emitter and collector are tied through another metal (usually indium) "alloyed" by fusion in a oven.

    These transistors are not the fastest, on the contrary, but much better than the early point-contact models. They have decent audio performance and enhanced versions could reach some tens of MHz. But here, it's an audio-range device. Hopefully it can reach the speed of the quartz resonators :-)

  • Funny clock preamp

    Yann Guidon / YGDES08/23/2023 at 17:47 4 comments

    The signal generated by the crystal oscillators are, to say the least, weak and any influence (real or reactive) downstream will affect the resonator upstream. So the project has been blocked for years, among others, by the requirement of a very high input impedance amplifier. I have looked at differential amplifiers but it's pretty complex. If possible, it should be simple, right ? Well I have found one solution !

    Two high-value resistors, one cap and one transistor, can you do better ? Here is the sim !

    It is pretty neat and I simulated the high impendance with the 470K series resistor, just to prove the point. The series capacitor also helps separate the levels but there are many things to consider though.

    First : it takes "a while" to start up when fed with an appropriate signal. In the sim, it takes about 30ms to stabilise. This is because it uses a silly trick : the series capacitor must also "charge" to the right level and it takes a while, through the 470K ground resistor. But once is starts to conduct, the 10M feedback resistor keeps the average base level at approximately the conduction level. The duty cycle is controlled by the value of the grounded resistor, 470K seemed to work BUT this resistor also affects the input impedance !

    Second : I used a "near perfect" Silicon PNP model. Germanium will leak and spit noise, they drift with temperature, the bandwidth is not great... So the values might change and equilibrium is not certain, but the rough order of magnitude is here.

    Anyway the circuit

    • is pretty sensitive (I used a 1V input amplitude but it can be lower)
    • sips very little current, since the 470K passes 11µA max (10× less than leakage)
    • uses few parts
    • is easy to tune (the ground resistor might be adjustable and that's it)
    • amplifies greatly even when I limit hFE to 20
    • saturates nicely... 

    Further amplification stages are required, the lower the hFE the more stages.

    And now I realise it is very similar to one part of the circuit in log Crystal Oscillator (Germanium Edition). Except that this branch will drive a high-gain amplifier (then a current buffer), not a resonator.

    We'll see how it translates in practice.

  • Working bistable at last !

    Yann Guidon / YGDES08/23/2023 at 00:50 6 comments

    I was hanging out on a Facebook group dedicated to Minimalist computing (which is perfectly in line with the #YGREC8 project) and a retired engineer dropped a little schematic.

    Joseph Watson posted a circuit I have seen again and again, and consistently failed to make work : the venerable symmetrical bistable.

    But this time with parts values !!! And this is a working circuit, as proved by his pictures of the circuit boards for his homemade computer built in the 60s.

    This circuit can be easily reconfigured from divider-by-two to shift register :

    As we already know, this 3-stage Shift Register can be easily looped back on itself with one inversion (swap the positive and negative signals at one point) to make a 6-step Johnson counter. Which is exactly what a digital clock needs (for the decimal digit, and the unit digit needs 5 bistables) !!!

    So what are the issues ?

    • First, I've always had troubles simulating this circuit with CircuitJS. Well, I made my own version of the above circuit (which does not differ from many other versions I have seen before) and this one works (when you get the diodes in the right polarity!).

    Here is the link to prove it.

    I rounded the parts values to E3 and it passes the simulator, however it must be "bootstrapped" because it insists on initialising in a "stuck" state. That will be the job of a master reset ciruit.

    • Second : Germanium drifts to Vbe=0.2 or 0.1 when the temperature rises. Which makes this type of grounded-emitter circuit difficult to operate. The parallel capacitors on the bases might help solve this issue but I have considered adding a diode on the ground side to "shift" the level. The VceSat might not bring the base down to the desired value to stick the circuit to the new desired state. Maybe a degenerating resistor and/or a diffpair-like topology could help too.
    • Third : Speed. The RC constants might in fact slow the whole circuit down, but there is no choice because it's the only minimal circuit with identical transistor polarities. To get to 100KHz, a careful design is required : trying and choosing the appropriate resistors and capacitors... Not too large, not too small..
    • Signal voltage swings are not characterised (over Vcc and temperature) and this will be another challenge. Here again, the capacitors will help, but also impede the frequency...

    So this circuit brings in quite a lot of "analog design" but we can start from the transistors themselves : the above 2N414 are not far from the OC70 : they both are alloy junctions.

    Some specs of the 2N414 : 3MHz, 24pF, hFE>60, 15V, 200mA, 200mW

    The OC70 is more modest and I'll tune all my circuits for 10mA Ic and 1mA Ib to be more consistent with other, speedier references (because I want to use AF240 later).

    From these values, one can deduce several values, and I'll keep the Vcc at 5V (because). So to get about 10mA at 5V, that's a 470 ohms resistor for the collector.

    The Ib is 1/10th of the Ic so the base resistors are 470*10=4K7. Awesome.

    There is a pull-down resistor for the base, that

    1. keeps the base at a low value when OFF, though it might not be low enough and the 10× value might slow down the off-turning. This is where "shifting" the emitter could be useful, as it would provide the pull-off resistor some headroom to totally discharge the base.
    2. limits the voltage on the base : 5V is applied to the base through 470+4K7 (that's 5K overall) but the 47K prevents the voltage from exceeding about 0.5V (in continuous operation). At 0.5V, the transistor can be considered "fully on"...

    I'll have to check degenerating resistors, either individual of common, to keep the circuit from saturating too much. Using 100K instead of 47K for the pull-off resistors would be OK with 0.5V of degeneration, which means 47 ohms... Aaaannnnnnd this makes the circuit unstable... It's solved with a common resistor though.

    There is another problem that the simulator does not let me estimate : the effect of the...

    Read more »

  • More Germanium lemonade, OC70 edition

    Yann Guidon / YGDES07/11/2023 at 00:07 0 comments

    The log 29. Germanium lemonade covered the OC139 in my stock. I only have 70pcs of this NPN type, but I have significant reserve of the PNP type and it's time to break the suspense. Let's bin some !

    hFEVbe mV
    Ic mA
    Ice0 mA
    Ices µA
    147
    212
    6.4
    0.13
    7
    235
    199
    6.6
    0,23
    25
    326
    214
    6.6
    0.35
    44
    427
    95
    0.5
    0.2
    23
    530
    213
    6.6
    0.33
    40
    625
    210
    6.6
    0.26
    32
    739
    194
    6.7
    0.2
    19
    819
    220
    6.5
    0.31
    30
    934
    207
    6.6
    0.35
    35
    1028
    213
    6.6
    0.23
    33
    1122
    222
    6.5
    0.20
    25
    1221
    239
    6.5
    0.12
    18
    1326
    223
    6.6
    0.28
    47
    1434
    194
    6.6
    0.25
    31
    1530
    104
    0.7 ?
    0.37
    31
    1635
    95
    0.81
    0.44
    52
    1732
    220
    6.6
    0.37
    40
    1834
    97
    0.64
    0.30
    35
    1932
    211
    6.6
    0.4
    45
    2045
    107
    0.8
    0.35
    30
    2134
    195
    6.6
    0.23
    30
    2242
    204
    6.7
    0.25
    20
    2333
    102
    0.71
    0.36
    35
    2437
    196
    6.7
    0.35
    46
    2523
    220
    6.5
    0.33
    45
    2635
    193
    6.6
    0.31
    31
    2737
    203
    6.6
    0.31
    30
    2829
    199
    6.6
    0.37
    49
    2929
    212
    6.6
    0.35
    41
    3032
    94
    0.75
    0.41
    48
    3130
    103
    0.77
    0.45
    45
    3231
    98 /200
    0.57 / 6.6
    0.25 /0.16
    14
    3325
    92
    0.48
    0.22
    32
    3426
    210
    6.6
    0.33
    44
    3526
    200
    6.6
    0.29
    30
    3628
    210
    6.6
    0.44
    45
    3731
    203
    6.6
    0.40
    52
    3827
    88
    0.61
    0.32
    41
    3929
    93
    0.70
    0.45
    62
    4025
    218
    6.5
    0.34
    54
    4141
    110 / 210
    0.73
    .26
    20
    4232
    230
    6.6
    .39
    49
    4320
    224
    6.5
    .32
    59
    4429
    207
    6.6
    .19
    18
    4544
    102
    0.89
    .43
    41
    4634
    197
    6.6
    .24
    29
    4733
    187
    6.6
    0.25
    28
    4834
    207
    6.6
    0.23
    24
    4934
    216
    6.6
    0.29
    34
    5046
    103
    0.70
    .22
    18
    5123
    209
    6.5
    .39
    54
    5225
    229
    6.5
    .22
    32
    5332
    193
    6.6
    20
    31
    5429
    210
    6.6
    .38
    48
    5525
    98
    0.74
    0.37
    44
    5647
    108
    1.0
    0.5
    35
    5728
    225
    6.6
    0.25
    32
    5838
    198
    6.7
    0.37
    37
    5926
    206
    6.6
    0.36
    57
    6044
    190
    6.7
    .35
    34

    There is this grouping of Ic at 6.6mA and then a few around 0.6mA, which corresponds to Vbe around 0.1V. So maybe this is a batch of mixed bins. However items #32 and 41 measurements show that the values vary randomly so maybe it's it's the tester...

    hFE is at least 20, sometimes more than 40. there is not much apparent correlation with Vbe. Remember that these values vary with temperature and it's now 27°C  (ambient). The Ice0 and Ices seem somewhat proportional, the have a 50% variability between consecutive tests but it's in the same ballpark.

    Overall, despite the quite low Vbe, it's a good batch and not a bad lemonade. Maybe the rumor is true, these are recently made OC70s from a new factory ?

    Now the other question is : how fast does that tranny switch ?

  • More inspiration

    Yann Guidon / YGDES01/20/2021 at 01:56 0 comments

    As mentioned in #Bipolar Discrete UART  I am in awe when watching this fabulous build :

    The most interesting part is at 15:50 and I have examined and even simulated this circuit at An even better SCR-based sequencer. This is an impressive design that inspires me again because I want to turn it into a Johnson counter, which is a special case of shift register, which is also something needed for the #Bipolar Discrete UART ...

    The name of the game is minimalism ! As noted before in 25. Germanium is not for ever..., the number of available vintage parts has dramatically shrunk and their price has exploded, so the fewer parts, the better !

    The design that Leo chose has 1P1N per count: that's 20 transistors per digit, where a Johnson counter would use only 1P1N×5=10 total, which would use only 48 transistors for H:M:S.

    Transforming the SCR latch sequencer into a shift register is not trivial but it should be possible. This would be also a great thing for the UART, because there would be no "slave latch". Looking at the schematic/diagram, which looks like a transistorized Dekatron, the clock pulse is driving ALL SCR through one shared diode, and "current steering" (something similar to the effect of a differential pair) will send the most current to one of the branches, which is pre-selected by the charge of a capacitor.

    This is this individual branch that must be tweaked, adapted, transformed, so it behaves like a D-flip-flop. Then it will be useful for a wide range of circuits :-)

    I know I should look more carefully at the works on the Shockley diode. More early SCR research can be found at https://www.rfcafe.com/references/electronics-world/transistors-negative-resistance-electronics-world-june-1969.htm

  • Germanium lemonade

    Yann Guidon / YGDES03/08/2020 at 05:35 0 comments

    See the update at the bottom...

    ...

    "When life gives you lemons, make lemonade" they say. This whole project is about "how did they manage to make lemonade back in the days ?"

    To understand this, I explore the old technology and parts "from back then". In this page I try to evaluate the quality and variance of the 70+ OC139 of my stock.

    They come from two sources and I was curious : do they come from the same batch ? Have they been already binned ? How much do they differ ? Is the leakage so bad ?

    The OC139 seem to be really "vintage", looking at the oxidation of the leads. Date code seems to be around 1961.

    Measuring the leakage is a pretty big deal because it badly affects the gain displayed by simple hFEmeters. Look at http://www.geofex.com/Article_Folders/ffselect.htm for the extended explanations.

    I didn't use my multimeter this time, but a handy little Chinese-made tool that guesses the type of tripole and its characteristics, which I wrote below.

    I bought this device at a local store with the usual markup (welcome to France) but I needed it to test my old capacitors and it has other useful features so I didn't care that much. And it was sold by an old, reputable store :-)

    The gain itself is not a big issue, as long as it's about > 20 and there is no point if it is >40 for this specific application. It's also good to see which parts are real lemons and should not be used in a circuit. For example, too high a leakage will disrupt my circuits. We have totally forgotten to take leakage into account in this century !

    Measuring these parameters is not an exact science since germanium is very sensitive to heat (even from the fingers) and even to light (the black paint can't stop all the light if it's intense enough) so sometimes I had to make several measurements.

    minifux1 :

    hFE Vbe Ice0
    106 210 5
    34 224
    31 204 7
    156 219 1
    193 21 164
    ???

    36 232
    29 229
    36 248
    32 132
    30 115 14
    44 167 14
    40 195 7
    32 239
    36 131 1
    120 195 7
    46 215
    86 200 7
    26 213
    38 210
    33 268
    31 219
    48 124 4
    49 195 14
    21 210
    30 200 7
    22 224
    31219 14
    173 161 35
    26 205 5

    ampliatubes:

    hFE Vbe (mV) leak (µA)
    40 126 4
    59 205 7
    42 220
    37 200 14
    23 221 8
    34 214 14
    42 219
    24 232 1100
    26 213 5
    34 229
    34 220 1
    28 216
    26 215
    40 204 7
    ?? 196 200
    79 197 8
    33 124 5
    95 220
    73 155 14
    49 215
    29 233 14
    44 137
    134 214 7
    124 159 8
    28 210 2
    46 229
    220 156 35
    37 211
    31 133
    42 204 14
    46 222 4
    296?? 218 11
    424
    188
    35
    40
    205
    7
    90
    126
    7
    52
    205
    7
    46
    135
    2
    31
    220

    464
    194
    34
    223
    174
    28
    22
    224

    26
    220

    72
    200
    5

    Verdict : one totally rotten lemon, several in bad shape, most are bitter but usable, but some have interesting characteristics and demand more examinations. Is their high gain real or an artefact ? and if they really have such a high gain, can they be used for more noble purposes than digital switching ?

    I also wonder about those parts with Vbe < 200mV.

    I didn't/couldn't check for the gain-bandwidth product (or rise and fall time). That should be for another time and for the high frequency dividers :-D

    I guess about half of them would be used for the intended circuit (the shift registers, I need gains between 20 and 40 and no significant leakage). I might have to get more of them to complete the circuit because there are quite a lot of stages... but they have become so expensive !

    Next step would be to plot the data in a graph and re-bin the stock, according to the various groups I identify in the dot cloud.

    And yes, germanium is fun but silicon is so much...

    Read more »

  • Reduction by mirroring

    Yann Guidon / YGDES03/02/2020 at 02:28 0 comments

    The previous logs Pulser-sequencer and Towards a smaller shift register try to reduce the complexity (and parts count !) as much as possible but the last circuit was still pretty daunting and looks overkill. I couldn't figure out what was feeling wrong until... I tried to reverse the circuit, and that would save a whole layer !

    So the new version both does the sequencing AND pulls the pass transistor bases. In the real/final version, the only transistor per bit will be a NPN, and it saves a bunch of auxiliary parts.

    I added another transistor (+1D1R) at the start to format the input pulse length and the curves show

    1. very short pulse (it works nicely)
    2. long pulse (it works well too)

    So far the cost is 1T 2D 1C 2R and the pass transistor would have the pulse-shortening circuit...


    So the circuit is completed with the 2K2 pull-down replaced by the pass transistor and its RC cell. Here is the circuit :

    My inventory shows I have a quantity (tbd) of 5K6 and about 100× 2K4. The pulse width ratio is given by the ratio of the capacitor values. Here we have 1µF / 220nf so it's approx. 1/4 to 1/5. This provides a niiice clean edge ! If I find a large quantity of cheap non-polarized capacitors at about 1µF, I'll put 2 or 3 of them in parallel on the sequencer side, and only one on the pass transistor.

    The power consumption is still very low when idle, and it can work for the slow parts : seconds, minutes, hours.

    Note that for the sake of evaluation, the "pass transistor" here is a NPN with 1K to the positive rail but the final circuit will have the polarity reversed and the pass transistor (a PNP OC70) will not be tied to ground but to the other latches. I expect that the sequencer-side OC139 will work well.

    The cost so far : 1P 1N 2D 2C 5R (11 parts, ignore the 1K pull-up)

  • Pulser-sequencer

    Yann Guidon / YGDES02/29/2020 at 21:48 0 comments

    Remember the last logs : the goal is to use as few transistors as possible to send a string of consecutive non-overlapping pulses to several pass-gates. Here the design uses NPN as primary type but it will be reversed later because PNP are the majority type in Germanium and NPN are getting hard to get...

    The last log Towards a smaller shift register has explored several methods but nothing satisfying yet.

    Today I tried 2 new tricks :

    • Feed the output back to the input
    • use diodes to separate the stages  and hopefully prevent the simulator to amplify spurious activity.

    The first result is there :

    The down and up edges are pretty clean though the output has a sort of slant after the first half of the pulse.

    There is one great advantage here compared to the previous versions : the cell is triggered by a positive-going pulse, and the idle state does not draw any current. This saves power and reduces drift, compared to the almost-always-on earlier version.

    The "cost" is 1P 1N 2C 3D 6R and can still be tuned.

    However when a resistor is replaced by a diode (to make a sort of charge pump) the result is even more interesting because 2 phases appear (source) :

    The trailing edges are not as sharp but they are now significantly separated, there is a short pulse (going to the pass gate) and then the output to the next stage happens.


    Apparently the sharpness of the trailing edges are not a critical parameter : (source)

    I changed all values to 4K7 and it seems to help a bit.

    I wonder if/how this circuit could be simplified...


    Trying to simplify the circuit and going back to the "first principles", I get this sequencer :

    Falstad did some really strange things with the "charge-pump-like" diodes and capacitor, like creating one pulse of the low AND the high going input pulses, so I had to restart from a clean empty page and compare with real circuits (just to be sure).

    The wave shape of this 5x sequencer doesn't look different from the previous one but it is way cleaner than the early attempts. Now I doubt that the feedback and more diodes are required.

    Note that the capacitor "pull-up" resistor must be significantly smaller than the transistor's base resistors because otherwise, the "going-high" front will make a resistor divider equivalent through the capacitor, which reduces the effective voltage range on the divider network and reduce the pulse time.

    The power is kept rather low, with about 5-8mA during activity, and mostly no current when idle. Only one cell is active at a time, except during transitions. The current is only dependent on the above-mentioned pull-up resistor that charges the capacitor before the up-going front when the transistor is released. That can easily be halved with a higher resistor (2K2) and/or a lower supply voltage.


    Adding a simple complementary common-emitter cell creates overlapping pulses :

    Adding a simple RC cell shortens the output pulse. The shape is not as sharp as I'd like but it's a minimal working circuit :

    This saves quite a lot of diodes, compared to the circuit at the top of this page. And the feedback is not even used.

    So it's working, the required power is reasonable, the pulses do not overlap and I can control the pulse widths with the corresponding RC constant...

    I tried to remove the diodes but the sequencer would be much less reliable. This output drivers seem to work without diodes but the trailing edge is not clean.

    However, adding one diode as feedback brings some advantage :

    It prevents the capacitor from discharging, until the PNP's output goes to 2 diode drops. The rising edge is delayed until a safer output level is reached. This prevents overlapping conduction for the rest of the circuit, AND both base resistors can now have the same value (they are 2×10K or 2×4K7 but now this difference is not required).

    This new version also adds a series  diode to the output buffer, to ensure that the voltage...

    Read more »

  • Towards a smaller shift register

    Yann Guidon / YGDES02/28/2020 at 01:58 0 comments

    (see updates at the bottom)

    _____________________________________________

    I seem to have solved the problem of cascading the latest flipflops, using better decoupling (and some diodes ?). Here's the new circuit :

    For the "fast" parts, a pull-down resistor would be required on the base of the pass transistors, to evacuate the base charges and "cut hard".

    There is a better Power On Reset as well, and this system only uses 6 transistors because there is no need to invert the feedback data (just use an inverted value).


    Then the challenge is to properly sequence the pulses to the pass transistors.

    The question here is not to control a master and a slave latch, but a series of consecutive latches ! so there are as many pulses as there are latches. Here I focus on the "slow" part (< 1Hz update) with a string of one-shot pulsers :

    I have really NO IDEA why the last stage emits multiple pulses... The mysteries of Falstad...

    But the principle seems to be realistic : each bit of the shift register uses 2 T for the FF, 1T for the pass transistor and another for the pulse/delay. It's far from perfectly working but there is hope that each bit uses only 4 transistors. I might add some diodes to create a charge pump or something like that...

    The "fast" circuits might need something more elaborate but at least I might have reduced the parts count for the H:M:S circuits ! (5+3+5+3+5+3)×4 (+ some control stuff) amounts to about a hundred transistors of the same polarity.

    I'll try to make it work, then move to the faster parts : I have found a gorgeous vintage resonator at 2K5Hz !

    That removes some pressure on the divider's design...


    Update : That might work but the simulator is losing its sanity...

    Sometime it wants to find crazy negative voltages at the collectors of the PNPs.  I'll have to test it on the bench but it looks promising.
    I must also find a way to "shape" the pulses because the "decay" is not very clean. But i'm getting closer to my goal :-)

    Cost : 1 PNP + 1 NPN (so it's the same when the polarity is reversed), overall : 5 transistors per bit of a shift register. For a whole display : that's about 120 + 6 transistors... This also facilitates the setting of the time because each shift register can receive a pulse, that could be from a button, and it's inherently debounced.

    Stay tuned !


    Thanks to Google Image search, I just found this :

    The page shows various enhancements to the system. I'll have to test it to improve my sequencer ! However if this trick works for 2 transistors, I wonder if/how it can work for more...

View all 35 project logs

Enjoy this project?

Share

Discussions

add_ocean wrote 09/26/2017 at 21:52 point

Well, let me add some ideas :)

While i studied "yet another discrete clock" project (very neat D-type flip-flops and Johnson counters), i must admit that binary logic is best in that it is very reliable and tolerates components drift but at cost of complexity.

Is actually binary a must? Why not to have "analog" appliance, at least it will be an unusual approach.

This is schematic of divider (from book described supposedly tested designs of amateur builders):

https://ibb.co/bz1hm5

There are oscillator and two stages of divide by 10. It says that each stage can divide by max 7 with ferrite cores, and by max 13 with now obsolete Al-Si-Fe cores (huge 36 mm diameter, low mu, low frequency, high flux. I believe modern iron powder might go just as fine). First coil is 0,33 Henry and next 3,3 Henry. Of course main disadvantages are complicated adjusting tank freq. and need for thermal stability of LC tanks (i believe 2,5% or better in whole temperature range ). Pobably need for careful  temp compensation?

Then, simple ring counter that drives LEDs, no binary D flip flops. More ring stages but much simplier each stage. Schematic from somewhere:

https://ibb.co/mY8Tb5

I am so sorry to show schematics that i did not try myself, so please forgive if these have some flaws. :)

  Are you sure? yes | no

Yann Guidon / YGDES wrote 09/26/2017 at 22:18 point

oh, you mean to tune a LC tank to the desired frequency ? That's... not reliable enough in my book :-/

I couldn't make sense of all the circuits, they surprise me a lot and understanding them will take time... But it's a an interesting puzzle/challenge :-D

  Are you sure? yes | no

add_ocean wrote 09/26/2017 at 22:53 point

Putting this design into industry grade device will require high end, rock stable LC tanks, i suppose. And, i see it now, below 20 Hz it will be even less feasible as inductance rises, and not to mention core materials won't work fine at such low freq. :(

  Are you sure? yes | no

Yann Guidon / YGDES wrote 05/10/2016 at 12:41 point
I'm still "sourcing" transistors. Hundreds of AF137, G106T, AC125V, OC602, AF200...

And probably the weirdest : unmarked OC70, that look like it was made yesterday.

Apparently, "germanium is a thing" like vinyl LPs, factories seems to be restarted !

Anyway I have enough stock to work on 4T flip-flops.

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 13:32 point

ebay has a lot of similar stuff - I bought a bag of Russian MP-transistors which are the same germanium retro like 2N1xx. They have a nice "feature" - you can use pliers to deform its head and then you can remove it completely - inside it will be a bare P-N-P (or N-P-N) assembly that is LIGHT-SENSITIVE ;)

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 13:35 point

OMG ! I will try :-D

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 13:48 point

I remember article from soviet magazine for kids where authors built "solar panel" out of a few dozens opened MP-transistors that generated about 2V on sun ;)

P.S. I found it:

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 13:53 point

This is a table from the same article with experimental data about what single diode (two columns on the left) or single transistor (two columns on the right) can generate from light (voltage and current):


http://uchifiziku.ru/2010/12/10/solnechnaya-batareya/

P.S. Full article:
http://zhurnalko.net/=sam/junyj-tehnik-dlja-umelyh-ruk/1986-08--num2
http://zhurnalko.net/=sam/junyj-tehnik-dlja-umelyh-ruk/1986-08--num3
Interesting fact that I didn't remember - author of this article is a woman :)

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 14:25 point

Awesome ! Thank you :-) I will certainly reuse this material so I'll need more infos :-)

If you have other "ideas" about them, please share ! For example I found this "logic gate"

http://www.seekic.com/circuit_diagram/Basic_Circuit/PNP_SERIES_TRANSISTOR_GATE.html


  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 14:51 point

Sure ;)

Another article series from the same soviet magazine was about building logic elements from those transistors (because they were very popular in Russia of 80s):

http://zhurnalko.net/=sam/junyj-tehnik-dlja-umelyh-ruk/1983-03--num11

Here you can see NAND3 with open collector (блок А), NAND3 (блок Б) and trigger (блок В) that actually constructed from 2 NANDs:


  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 15:02 point

@Alexander Shabarshin awesome, thank you !

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 15:19 point

And these accidental memories made me curious how fast such NANDs could run ;)

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 18:02 point

OK, I built it :)


It's MP25A p-n-p germanium transistor (similar to 2N189) manufactured in USSR in September 1979 (I got bunch of them from ebay relatively cheap) connected as 2nd circuit from article (NAND element), but instead of one diode V4 I put 3 silicon diodes connected in series (the circuit refused to work with 1 silicon diode as V4) and I use 10K resistors. According to spec MP25A should be able to work with frequencies up to 250 kHz, but this particular circuit has a limit about 10 kHz - see oscillograms for 5,10 and 20 kHz:




  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 19:44 point

I put 4 diodes to the base circuit in order to shift threshold lower:



Then I put capacitor 480nF over the diode series and resistor from base to emitter 1K - as per @matseng

https://hackaday.io/project/6668-aytabtu-discrete-computer/log/23923-more-speeeeed 

and I got nice 100 kHz :)

P.S. Reducing voltage to 4V actually allowed 200 kHz signal to be processed:


and U-curve is more natural with 4V (threshold closer to U/2):


  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 23:35 point

It seems we got a 2nd contributor here ;-)

I haven't received my eBay orders yet (it will take a while) so I hope that @Alexander Shabarshin will make a proper log page to describe these experiments :-)

Thanks for your precious time !

  Are you sure? yes | no

matseng wrote 04/03/2016 at 14:51 point

On the other hand any silicon BJT is also light sensitive. I remember cutting of the tops of TO3 encapsulated 2N3055's and using them as foto sensors when I was a teenager back in the late seventies.... I think that they actually generated quite a low of power in bright light.

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 14:54 point

These monster transistors are more difficult to open I assume...

  Are you sure? yes | no

jaromir.sukuba wrote 04/03/2016 at 18:24 point

Oh those yellowish scans from Russian magazines bring back the memories to five issues of Modelist-Konstruktor magazines I bought for 3 Slovak crowns (~= ten eurocents) from my schoolmate - back in 1993 - I was in third grade of elementary school. Funny thing is that I didn't understand a single word, I didn't even understand Russian alphabet. My father learned me it in one Sunday afternoon, so I could somehow read the articles (one in five Russian words resembles somehow equivalent Slovak word). That was the time when I got fascinated by electronics.

The M-K magazine had similar look & feel.

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 20:29 point

Yes, I remember Modelist-Konstruktor, but I don't remember any article from it :)

  Are you sure? yes | no

jaromir.sukuba wrote 04/03/2016 at 12:08 point

Having a bag of 500+ germanium switching transistors, this looks like the right pointless project for me!

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 12:55 point

are they for sale ? :-P

  Are you sure? yes | no

jaromir.sukuba wrote 04/03/2016 at 19:14 point

Don't ask hoarder to sell his sacremental ;-) though you can take a look at part of my collection

https://picasaweb.google.com/111890741167251011072/April32016?authuser=0&authkey=Gv1sRgCOfWztP075KM-QE&feat=directlink

I must admit I'm slightly obsessed with germanium components.

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/04/2016 at 00:17 point

Well then thank you for your kind participation :-D

Would you like to use some of them to help with this project ? :-)

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates