So how would I build my own Batt-O-Meter?

[Steve A.]

I'd seen these listed in one of those catalogs that keep giving me G.A.S. and I figured that it should be fairly easy to make up a rig that would do the same using your own DMM. It uses a 1/4" stereo plug that would go into the input of a pedal or the output of a battery powered guitar. So it should add in a load to measure the voltage from ring to the sleeve, and also be able to connect the ring and sleeve to the DC ammeter section of the DMM to measure the current draw of the FX or circuit. I believe that the Batt-O-Meter will also predict the hours remaining on a battery, but we could use a chart for that and skip the circuitry. Or do you think that the B-O-M is able to measure the mAh remaining in the battery?

The Batt-O-Meter retails for $30. Here is a link:

Overview

[cjlectronics]

I've been mulling over this device for a couple of days and just can't realize how they do this. I have hit a wall with how they measure the battery voltage through the signal input. Either, I am due for another learning venture in electronics or we are being manipulated by a great marketing scheme.

So far, from what I gather, the only way they do this is by using a special plug (which they have) that when fully inserted makes contact with the battery's negative pole in the jack and the other contact on the plug to the ground of the pedal... chassis ground. I've never done this but I would suspect you will measure a voltage potential? If this is true, then you can supply a load and sample the battery capacity, voltage level, etc. If this is true, this is why the device doesn't work with all pedals because not all pedals are configured where the negative battery pole is switched with the input jack.

If this is not how this is done then I'm drooling to find out how they do it!

[J M Fahey]

They are measuring the battery *voltage* , that's the only certain thing they do.
They probably also measure the actual mA used.
They probably use the pedal itself as a load, you can't get more realistic than that !!!
They probably have a built-in "lookout table" comparing actual voltage under load plus mA used , to give you a statistical estimate of remaining life, in hours or minutes.
The only data they can't read, battery type, *you* supply via a slide switch or similar method.
It probably can be done with one of those newfangled funny inventions, a PIC or similar chip.
No, a NOS Telefunken Gold Pin E83CC won't do here.
PS: the seemingly overused qualificative "probably" comes from the obvious fact that I have never even seen one in the flesh.
And consider $30 a fair price for this, a *very* specific multimeter, which seems to do its single trick very well.
Kudos to the designer.

[52 Bill]

We had one of those in the store when they first came out. Seemed like a reasonable device. Keith McMillan is the original guy behind Zeta instruments and amps, and the Little FEANC onboard active guitar system.

Follow the link and click the support section tab. There's a lot more detail as to what and how, etc.

[Steve A.]

GC was selling one of these for $19.99 on clearance last week so I bought it. They are normally $30 but $20 is a much better price point for something like this- the cost of 8 alkaline batteries that you might have thrown out not knowing how much life was left in them.

Simple things first- there are two tabs on the outside to check a bare 9V (or 1.5v) battery. There is a 3 way switch for alkaline, zinc carbon and rechargeable. So far you do all of that with a Radio Shack battery checker. The real trick is measuring the voltage inside a pedal or active guitar/bass. There is a stereo plug that goes into the input and when you push the test button it will go through its cycle like "AL | VOL 8.60 | HR 62". During the test the pedal LED will light up briefly while the tester measures the current being drawn. And based on the battery type and voltage measured it will predict the number of hours left on the battery, which is very good to know when you are setting up for a gig. There are many times when I would change the battery "just to be safe" when it probably had many hours left on it. With this tester you can tell the real hogs- like my digital delay pedal and Malekko Spring Chicken reverb- and seriously consider using an adaptor with them.
For 1.5v batteries you put the + end to the + terminal and press the tip of the stereo plug on the - end. The tester automatically switches from 9V to 3V to 1.5V and will tell you the voltage (presumably under a typical load) and the percentage of life left (PRC). Methinks that Keith had a special chip made specifically for this device.
You can do much of the same testing with a stereo plug and a DMM that also measures DC current. A typical stereo jack used to switch on the battery in an effect has the negative battery terminal connected to the ring and when you insert a mono guitar cable it will connect that terminal to ground. So you can measure the voltage between the ring and the sleeve, but you should make sure that there is a load to get a decent reading (hint: resistors will work). You can also measure the DC current between the ring and the sleeve with the pedal set to on. And then compare that to the milliamperes that the battery can deliver when fully charged.

Steve

P.S. You can also use this device with those cheap 9v batteries that Walgreen sells- 6 for $10 on sale. They don't last as long as the premium brands and they always seem to fail at the wrong time. With the Batt-o-meter you get some idea whether it (and you!) will die on stage that night.