I'm working on an amp-hour meter (actually milliamp-hour) and am planning on using an Allegro current sensor to measure current from a discharging battery under load. I plan on displaying the accumulated amp-hours on an LED display, and a PIC will be running the show.
Is the Allegro the best method for doing this, or is there another way? I haven't gotten into it yet, but it looks like the Allegro takes some calibration to make it accurate.
Any suggestions? Thanks.
Since you are measuring mA (you don't mention how many) you should chec out the FAQ on the allegro part
Given the low resolution and accuracy issues, and assuming that you ar sub 1Amp, I would reccomend that you measure the voltage across a curren shunt. Maxim has a part that will allow an external current shunt National has one with an internal one. I think TI (Burr Brown) & Linea Tech also have products. Here's a start at Maxim.
But you don't need a dedicated part- you simply need a differenc amplifier that can handle input voltages beyond the supply rail. You ca make your own with resistive dividers at the input, or use a product lik the AD626, an Instrumentation amplifier from Analog Devices. Of cours this approach is not isolated.
I am currently using the Allegro ACS704xx-005 current sensor and I hav developed I problem where the device "locks up". I am awaiting tec support to find out where the problem lies.
-Aubrey This message was sent using the comp.arch.embedded web interface o
Maxim has a few battery "fuel gauge" devices.. real low power..
About a million years ago, I built a mA hour (actually a uA hour) meter using a voltage to frequency converter. There was an app note on a Analog Devices part that we used in a configuration for measuring current (I don't remember the part number). The neat thing is that it will integrate any peaks or spikes between output pulses, and has a very wide dynamic range (especially if you trim any ofset errors). We wanted to know the long time power consumption of a device that drew uAs in sleep-mode, and mAs when it had something to do. If it's for lab use, just connect a frequency counter and a few passive parts and you're done.
-Hershel
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.