dc voltmeter with memory

[hobierp]

I have no idea about electronics. I approached a prototype company and they suggested I try this on my own as it would be too small for them. So here is what I am wanting. A dc voltmeter that has memory. The application is to measure voltage while a circut is in use, and the user is not there to watch the display. The need is to be able to measure the lowest voltage between resetting of the memory. I would like to be able to view the current voltage, then view the lowest voltage the circuit saw, and finally be able to reset the minimum so a new value can be read and saved. The system would hopefully be able to use the source it is measuring or if neeeded a small external battery. Weight, size and waterproofing are constraintsts.
I would be using this to "watch" a battery pack in the range of 4-10 volts with a capacity of about 2000 mah. The reason I need this is when the stress on the system gets too high the voltage is dropping below what I am wanting it to be. If I can see what is happening in the system I can make a better decision of when the batteries need changed.
I know there are lots of voltmeters listed, but I have yet to find something that works like I am wanting. Any help would be greatly appreciated. Especially if the reply is in something that someone that knows nothing about electronics can understand.

 

[vne147]

Would something like this not work for you? It's a multi-meter that you can hook up to a computer through a serial connector. The included software will save and or graph the measured values.

Digital Multimeter W/RS-232 Interface Model MAS 345

 

[hobierp]

Not really. I read on a different thread where someone wanted a digital voltmeter for a RC plane. This would be used for something like that. You want to be able to look at the voltage while the plane was sitting there before take off and look again when it landed. But you would also want to know what happened while it was flying. If you had 6 volts sitting there did the voltage stay at 6 volts or because of the stress on the wing surfaces and the servos trying to move them, did the voltage drop to accomodate the current the servos drew. By knowing how far down the voltage dropped you would then know when to change out your battery pack.

 

[ParkingLotLust]

You could do this with a microcontroller and voltage divider to drop the voltage to a 0-5v reading. The reading at the analog pin could be logged as often as you want.

 

[kchriste]

Here is another meter with this built in. You don't need a computer interfaced with it, but it is capable of that too.
**broken link removed**
If this is going in an RC plane, then the meter above is much too large unless the plane is big too.

 

[hobierp]

Kchriste - thanks for the thought but I am not looking to spend that much money on something. But that did give me some ideas on searching more. I came up with a book called Microprocessors and microcomputer based system design. In chapter 10 it talks about what I want. So I may look into that and see what I can figure out from there. Has anyone looked at it? Is it too old or would the chips it is talking about be available?

 

[vne147]

I have not looked at the specific book that you mentioned but you could definitely accomplish what it is you need to do using a micro-controller. I didn't suggest this at first because you started out this thread by saying you have no idea about electronics so it seemed to me that going the micro-controller route would require a fair amount of learning on your part to get up to speed. Nevertheless, if you want to pursue this, and I encourage you to, there are plenty of tutorials on this subject throughout the web. Here's one:

A simple PIC LCD volt meter project.

You can probably get everything you need for this project for under $50. I don't think this project includes the memory feature that you discussed but that could easily be added with some extra programming.