djQUAN
0
- Joined
- May 27, 2013
- Messages
- 1,154
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- 63
There have been times that I needed to measure very low voltages (millivolts and sometimes down to microvolts) and my multimeter is a typical autoranging type with 1mV resolution which isn't good enough.
When I'm measuring low voltage drops across high current shunt resistors or contact points or adjusting bias currents in amplifiers, I needed a few digits below millivolts for accuracy.
Here's what I did in an afternoon to fill that need (without having to buy another multimeter) and using parts already at hand.
The parts: the familiar digital panel meter, switches, project box, dc-dc boards and connectors
cut the rectangular hole using my mill. I also used the mill to make accurate pilot holes for the switches and banana jacks.
Drilled the holes for the switches and jacks
Here's the meter wired up. There is a diode protection circuit to prevent blowing the meter input when a high voltage is accidentally applied. The grey pot at the switch is the cal adj for measuring the internal battery voltage to check for battery life. A step up converter board wedged on the side powers the 5V panel meter from a 4.2V lipoly cell.
I used a li-poly pack from a broken ipod touch. This li-poly cell is only about 2mm thick and has a protection PCB already. A 4pin female header is used as a charging port.
Adding some labels and here's the finished meter along with the dedicated ammeter that I made a while back.
I calibrated the meter by wiring it in parallel with my calibrated multimeter to a resistor voltage divider which is then connected to an adjustable bench supply. I adjusted the supply so the multimeter reads 199mV and calibrated the DIY meter to have the same reading.
The meter range is 0-199.99mV with 10uV step. It isn't lab grade but would get me by for those odd jobs that I need to measure small voltages. (if anyone is curious, the ammeter has two ranges, 0-20mA and 0-10A but it can measure up to 20A in the high range with short duty cycles. It also uses a li-ion cellphone cell and same charging port on the side)
When I'm measuring low voltage drops across high current shunt resistors or contact points or adjusting bias currents in amplifiers, I needed a few digits below millivolts for accuracy.
Here's what I did in an afternoon to fill that need (without having to buy another multimeter) and using parts already at hand.
The parts: the familiar digital panel meter, switches, project box, dc-dc boards and connectors
cut the rectangular hole using my mill. I also used the mill to make accurate pilot holes for the switches and banana jacks.
Drilled the holes for the switches and jacks
Here's the meter wired up. There is a diode protection circuit to prevent blowing the meter input when a high voltage is accidentally applied. The grey pot at the switch is the cal adj for measuring the internal battery voltage to check for battery life. A step up converter board wedged on the side powers the 5V panel meter from a 4.2V lipoly cell.
I used a li-poly pack from a broken ipod touch. This li-poly cell is only about 2mm thick and has a protection PCB already. A 4pin female header is used as a charging port.
Adding some labels and here's the finished meter along with the dedicated ammeter that I made a while back.
I calibrated the meter by wiring it in parallel with my calibrated multimeter to a resistor voltage divider which is then connected to an adjustable bench supply. I adjusted the supply so the multimeter reads 199mV and calibrated the DIY meter to have the same reading.
The meter range is 0-199.99mV with 10uV step. It isn't lab grade but would get me by for those odd jobs that I need to measure small voltages. (if anyone is curious, the ammeter has two ranges, 0-20mA and 0-10A but it can measure up to 20A in the high range with short duty cycles. It also uses a li-ion cellphone cell and same charging port on the side)