Help me in building the E-meter shown in this link

[Commander_Chaos]

E-meter

I'm a clueless newbie interested in building the "e-meter" shown in this link:

https://www.cs.cmu.edu/~dst/Secrets/E-Meter/Ralph_Hilton/Mk4.htm

Anybody here ever made one of these? I understand the schematic and the values for the resistors and capacitors, but some of the other stuff has me puzzled. It looks pretty simple, but I'm in over my head. The only other thing I've ever made was a distortion pedal for an electric guitar, over 10 years ago.

I'm not a scientologist, this is just a goof.

 

[keith1200rs]

E-meter

It looks pretty straightforward, if a little dated. Wooden box and old fashioned panel meters, although I guess they still exist. What parts do you need help with?

Keith.

 

[Commander_Chaos]

Actually, I'm building the fancy one with the metal box. I found a supplier for the needle meter.

I get that the "C" on the schematic is for capacitor, and the "R" is resistor, but what's the "TR" mean?

Also, the resistors I'm finding for the values shown are all rated at a 1/4 watt. Will that work?

 

[keith1200rs]

TR is a "trim pot". Normally they would be trimmers inside the box, but in this case they seem to refer to the front panel knobs. This would be what they look like (not PCB mounted):

https://www.radioshack.com/product/index.jsp?productId=2102789

All four opamps (the triangles) are in one LM324 package.

1/4 watt resistors will be fine - there is nothing that looks like it will dissipate much power.

Keith.

 

[Commander_Chaos]

Thanks, that makes sense. I guess I can figure out the op amp connections from the printed circuit.

More dumb questions:

Does the "sens" in the diagram refer to the rotary switches?
What does "PC" mean?
There are two wires that go to electrodes held by the "patient". Any idea where those connections are?

 

[keith1200rs]

What I said earlier about the trimmers was wrong. The trimmers are small PCB mounted multi turn ones - small grey blobs on the PCB. One of the panel potentiometers connects to the TA1/2/3/4 connections (not all at once - it seems to depend on whetehr you have one or two meters). The sensitivity pot connects to SENS1/2/3, presumably to the three potentiometer connections in that order i.e. SENS2 to the centre pin of the pot.

I think PC is where the "patient" connects. You can see the green wires to PC disappearing from the PCB in the photos.

One thing that isn't shown is the power connections to the LM324. Pin 4 is positive, pin 11 negative. I think it connects directly to the battery (across C2).

I have noticed that he does recommend a potentiometer **broken link removed** but any with the correct value will do. Make sure you buy a linear one, not log.

Remember to short SW2 or connect one of the resistors mentioned in the text.

Keith.

 

[Commander_Chaos]

Thanks a ton. This is enough to get me going. I'll post more questions once I get into it. You rock.