I have a blue-point eedm503b multimeter. I use it everyday at work and at home on my bench and I often forget to turn it off. So that leads to me keeping a lot of 9v batteries in my toolbox. I am wondering how hard it would be to build a small shut-off circuit that fit inside the meter and connect between the battery and the meters board. I would like it shut the meter off after an hour maybe. I could handle having to turn it back on after an hour of use. It would be really cool if it would shut it off after an hour of non use. But im not sure how I would make the circuit detect meter usage. Any thoughts? Im not asking for someone to build it for me, But I really don't know where to start and it has to fit my skill level. so Im looking for a few different ideas so I can work that part out. Thanks as always

 

I built a portable scope calibrator and included a circuit that latches power on for about ten minutes when you push a button then shuts off.

 

another 555 timer project..lol.. Ive had 3 projects in the last week that I used a 555 on..

 

any thoughts on a way to detect meter usage and have it trigger the 555

 

any thoughts on a way to detect meter usage and have it trigger the 555

That's going to depend on the meter and also what constitutes "usage".

For many meters with autoshutoff features, it based on sensing the last change in the meter configuration settings -- the last time a button was pushed or a knob was turned. It very seldom includes moving the probe plugs from one jack to another, let alone moving the probes from one measurement point to another.

In a mod, you will probably have to physically see which controls you can get physical access to and just have to live with being responsive to changes in that subset of the controls. Of course, you can always add a "refresh timeout" button and just get in the habit of occasionally pushing it while you're using it.

 

Maybe some kind of motion, position or vibration sensor?

 

I was thinking something like using the last time the leads completed a circuit could be used to trigger the reset pin of an lm555. It would reset the timer everytime so the hour would reset every time I tested something. you always use both leads to test anything from impedance to amps to ac/dc voltage. But however I try to make it work, it cant interfere with the meter accuracy. Is this doable?

 

The meters I've used require one to periodically move a switch to keep the meter on. It's rather difficult to detect meter operation for this purpose but it could possibly be done if you have a schematic for the meter. Detecting the signal on the leads is problematic since there is such a variety of signals to detect (AC, DC, resistance measurement, etc.).

Otherwise I would just add a small push button to reset the timer and turn the meter back on. For a 1 hour time a 555 timer might be marginal. Likely a better solution is to use an oscillator with a digital counter for the timeout such as here. You can replace Q1 with a P-MOSFET to control the power to the meter (source to V+ and drain to meter circuit), and eliminate the relay and associated components.

 

I was thinking something like using the last time the leads completed a circuit could be used to trigger the reset pin of an lm555. It would reset the timer everytime so the hour would reset every time I tested something. you always use both leads to test anything from impedance to amps to ac/dc voltage. But however I try to make it work, it cant interfere with the meter accuracy. Is this doable?

I agree with crutschow. Plus, it's going to be hard to interface with the leads in such a way as to not effect the measurement in at least one of the modes on at least one of the ranges. Further, consider that you might go from measuring a nanofarad capacitor to measuring a 240VAC power line and your circuit would have to be okay with either.

 

Yea I know, It was just a thought. I like the switch idea though. I was thinking about it today at work and I think I could deal with it just shutting off every 30 minutes or so. I don't usually have to monitor my meter for more than 5-10 minutes straight very much. Its usually more like 3-5 minutes per use. So if I had to turn it back on every 30 minutes, It would be that much different than I use it now. But I have a nasty habit of walking away and leaving it on. A 9v battery doesn't last long like that. Another hurdle is that it has a push button type power button. Without looking at the circuit board I was thinking maybe I could replace it with a momentary button switch an make it fit in the rubber button somehow,But that shouldn't be to hard.

 

On second thought, If I use a momentary switch the meter would turn off as soon as I released the switch wouldn't it? Could I use it to trigger the 555 to start the cycle? and after more consideration I believe a 15 minute cycle would be sufficient enough to conserve battery.