Velleman's LCD digital panel meter is designed as a digital DC voltage display meter for hobbyists and for industrial applications where accuracy is important. Over range indication informs a user of over-voltage conditions. Two to three readings are taken each second to ensure display reading integrity. For portability, this panel meter operates off of a 9V battery.
We use these meters on switching/power boxes on a cycle tester one for each station. And they work reliably when hooked up correctly to line voltage and meter power voltage. Voltage surges on the power kills this meter. Don't use Voltage dividers, they killed this meter in our application. So we have a switch in line with a 9V battery and turn the meter on only when we are verifying the settings are correct. Or you can use a separate regulated 9V power supply. The down side is that these meters are factory set at 0-2 volts and you have to remove RA & RB chip resistors and solder in the values in the instructions for ranges 0-20, 0-200 and 0-2000. There is a ranging resistor set you can buy, but MCM does not carry the set and they are rather pricey if you can find them. Also if you don't know how to solder SMD components you can destroy or damage the chip resistors. Metal film axial lead resistors 1.0% 2W work fine. Use a a 10 Meg where it calls out for a 9.9, 9.99 and 9.999 Meg. There are holes in the PCB to accept the wire leads, but the 10 Meg resistor wire diameter is too big to fit in PCB hole; so cut wire at 20~30 degree angle push in hole and solder. It takes a bit of fancy J-wire type bending in 3 axises to get the 10 meg to lay flat on back of meter PCB. I done it several times now, its do able just take your time. Though the instructions call out 0.5% or 1/2% tolerance our meters are right on with 1% resistors as checked with our digital hand held fluke meters which are calibrated every year. Currently, we are building spares boxes and making changes and adding a cooling fan for the power regulator board inside the box and we are sticking with these meters. We have had a few of these meters "wear out" or die, but because of the low price, we replace them and go on. In three years we have replaced 6 out of 13 meters. If you are looking for a long term display, this is not it, spend a lot more money. But a good cheap meter it is, if you don't mind setting the voltage range, but buy a spare display or two.
Inexpensive and works well. As received it makes a good voltmeter with an independent 9V battery. It can be used with a common supply if you know what you are doing. It apears to be based on the Maxim ICL7106 or similar. Look up the data sheet and pay special attention to the section on Analog Common which is tied to IN-. It is driven to the +PS minus 2.8V. It can be pulled lower easily but pushing it higher requires >30ma. The inputs have good CMRR but must be kept within the +PS minus 1V to Gnd Plus 1.5V. With a LM324 op-amp and a few resistors you can do almost anything.
To measure <20 volts, remove resisters RA & RB (it's a jumper). Then use a 10meg resistor for RB and a 100K for RA. Remove the solder bridge at P1 and add a solder bridge at P2. Don't forget the second terminal down is the +9 to 12 volts in... Works great!
This meter is good for the money. As stated previously, the measured power and source must be isolated or it will be DOA. Be sure to solder the connections. Does anyone know how to set this meter to 0 - 20 volt range? I believe you just need to solder in a resistor across RB and one across RA. Please respond with a comment if so, I'm sure feature buyers would appreciate it too.
Word of caution, DO NOT hook power up backwards, instant D.O.A. The power supply marking shows a shematic symbol of a battery, the longer dash is the positive. Also the power supply and voltage to be read must be isolated....
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