Re: Bob Parker's Blue ESR Meter Assembly & Comments
Here is a great description on how the circuit works and a schematic:
Your problem is probably in the LED display multiplexing circuit.
Check around Q13 for both correct transistor polarity and the proper value resistors in circuit. Both Q13 and Q12 are responsible for connecting all of the common cathodes on their respective display to ground.
When it's time to addresses display 1 Q12 conducts and IC3 then sends current to the proper segment anodes they then illuminate.
After it's done Q12 shuts off and Q13 comes on IC3 again sends current to the segment anodes. I believe this is how this circuit works. Someone correct me if I'm wrong.
This is done faster than the eye can see so it appears all segments on both displays are lit at once. This allows you to drive two displays with the same 7 segment anode lines and most importantly a single display driver IC.
Q13 is responsible for the second display. Without it the segments on that display can't illuminate even though they are being driven by IC3 on their anodes.
Hopefully the reason it's displaying 0 is because you're shorting the probes because it's supposed to display a - on the left display when they are apart.
Here is a great description on how the circuit works and a schematic:
Your problem is probably in the LED display multiplexing circuit.
Check around Q13 for both correct transistor polarity and the proper value resistors in circuit. Both Q13 and Q12 are responsible for connecting all of the common cathodes on their respective display to ground.
When it's time to addresses display 1 Q12 conducts and IC3 then sends current to the proper segment anodes they then illuminate.
After it's done Q12 shuts off and Q13 comes on IC3 again sends current to the segment anodes. I believe this is how this circuit works. Someone correct me if I'm wrong.
This is done faster than the eye can see so it appears all segments on both displays are lit at once. This allows you to drive two displays with the same 7 segment anode lines and most importantly a single display driver IC.
Q13 is responsible for the second display. Without it the segments on that display can't illuminate even though they are being driven by IC3 on their anodes.
Hopefully the reason it's displaying 0 is because you're shorting the probes because it's supposed to display a - on the left display when they are apart.
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