Close

Scoping the display driver

A project log for Fluke 8060a Custom LCD

I've had a number of 8060s with failed displays and always wanted to design a replacement... so I did!

ogdentoogdento 11/17/2022 at 05:020 Comments

The display in the 8060 is driven by a Sharp SM4a "4-bit microcomputer" which can do up to 68 segments with a 1/2 duty 1/2 bias drive.  I didn't have a clear picture in my mind of the waveform that drives the display segments so I poked around a bit with my scope.  

The drive signal is 0 to about -3.2v overall.  The segment waveform is a ~156hz square wave, and the H1/H2 are stepped and out of phase with each other.  When H1 or H2 and the segment waveform have a 3.2v difference (this will be for half of the H1/H2 cycle), that segment is ON.  The other half of the cycle has a difference of 1.3/1.8v and the segment is OFF.  The average voltage for the cycle is zero - otherwise the LCD would be damaged.

Here's a shot showing the drive signal for turning on the Rel segement, which is connected to the H1 common (notice that there is a delta of 3.2v - so it's ON - for 1/2 of the cycle):

Here's the signal when the segment is off (notice that no segments have a 3.2 volt delta):

Discussions