Test & Measurement interface for Soundcard

Has anyone successfully used a DK201 panel meter instead of the unobtainium original?
The pinout is different, but I'm more concerned whether the functionality is the same.

In the original MDMV000, the annunciators (inputs for e.g. decimal point, m, V etc) are driven by signal BP and BPN, short for 'backplane' and 'not backplane'. In the documentation for that display it says 'connect the annunciators to BPN for it to appear' i.e. turn on, and annunciators not in use connect to BP i.e turn off.

The soundcard circuit has the used annunciators driven by XOR gates, one input of which is BPN. So it would appear BPN is outputting a TTL level, is it some kind of strobe? Why is it necessary to use an xor gate driven by BPN rather than the switch directly?

The DK201 appears to have something similar, a 'BP' (backplane) and 'XBP' pin (referred to as annunciator and decimal point driver in the datasheet). Are these the same?

Having wired the display onto a breadboard, applied 5V VDD and connected s low voltage source to the input I can get the DK201 to read e.g. 1600 for 0.16v input which is correct, if I check the voltage on the XBP pin its about 60mV dc (no sign of a strobe signal). So very curious as to what the backplane signals are and how they work.

-Keith
 
I used the one attached, supplied by Mouser. It doesn’t fit any panel and needs to be hand wired to the original PCB but works as expected incl. decimal point without the need to change the original circuit.

P.s.
In my new design I replaced the whole thing by a combination of LTC1966 (true RMS converter), LT1494 (buffer) and 1706 (0-200mV, single input digital panel, supplied by Aliexpress). This won’t give you a decimal point which I ‘faked’ with four LEDs…
 

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I am in the process of redesigning the whole thing —for me…
Changes:
  • no SC output, only 2ch (stereo) input
  • all EOL parts replaced, different RMS measurement with modern parts, incl. new panel, cost effective

If you’re interested, PM me and I’ll send you my KiCad and LTSpice files. The build is not yet confirmed, I am in the process of putting it together and testing…

P.s. I have agreement from Pete to modify his design w/o commercial interest! Gerbers attached.
View attachment 1267899

Interested. I know I am being very lazy, but do you have a Mouser project for the new parts?
 
Unfortunately I don’t have one, since I ordered parts for three projects at the time…
But you can go with Pete’s BOM and strip parts for the SC output. The LTC1966 are modules from Aliexpress ($10 each) and the 1706 is a single input Panel (YB5135D Digital Voltmeter DC200mV) from Ali ($10 each) as well. The LT 1494 is a dip. I kept the other parts. Look at my schematic above nothing special…
The dual voltage inverter is a CUI Inc PUZ3-D5-D15-D (4.5-9V to ± 15V).

PM me and I’ll send you my KiCad files then you can run a BOM and/or make mods…
 
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Thanks, but the switch I have doesn't have a lock ring. It has two tiny, needle-like pins which can be put into small holes in the front of the switch. But although it's easy enough to work out how far apart they must be to get 4 positions out of the maximum, getting them so the range switch goes from the lowest to highest range isn't obvious.
 
RTFM, it’s all in there…
Or try and error, lol

P.s.
If someone is considering replacing the AD536 with modern LTC1966, you can get them from Ali, but be aware there are quite a few faulty modules sold. These modules won’t work out of the box because the PCB has an error since pin one of the LTC is not connected to GND. After running a small bridge these modules will also work flawlessly. Don’t skip the LT1494 buffer it’s required for smooth output (see application notes).
 
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