Docs on panel meters?

Hi Ethan It looks like this is a tough one. No one has responded. You may have to start doing some hunting with an ohm meter. It is most likely a dual slope A/D. These are quite accurate and simple. You might see if there are some common points on the connector that have the same resistance and polarity to the LED's. This would kind of give one a starting point. See if you can figure if the LED's are common cathode or common anode. Typically, the power leads are either grouped at one or the other end of the connector. The other is that they might be split with one lead at both ends. Most of the dual slope A/D's had diffential inputs such that there wasn't one lead tied to ground. This may have been different on the panel meters. They may even have the meter common tied to either lead of the supply so you can't assume that a common lead is the plus or minus. The input could even be tied to a divider to give the most common range. Some opamps could take slightly negative voltages and still work well. 200 mv is small enough that this might still be in the common range. I've used similar meters years ago and the one thing to note is that most require an isolated power supply. If there are electrolytics, at least one of the leads will most likely be tied to ground. These are not useful as part of the dual slope A/D circuit and would most likely be filter capacitors. Most IC's have diode protection on their input leads. These would usually indicate forward in the reverse direction that they were actually intended to be used in circuit. If you know the polarity of the LEDs, and you think you have the power leads figured, you can put a current limiting resistor in series and bring the voltage up slowly. Watch the polarity of the voltages on the LED's and electrolytics. Dwight _________________________________________________________________ News, entertainment and everything you care about at Live.com. Get it now! http://www.live.com/getstarted.aspx