Friday, August 26, 2011

Beginning the Current Sensor

I received another care-package thanks to my dear sister. This hobby stuff from the cruising world is slow and painful (if you are as impatient as me). The key additions this time are below. There seem to be several versions of the "helping hand", this one is not so much in the helping department. The little screws are very difficult to turn to tighten the rods. Then it slips with the pressure of the soldering iron. I couldn't tell from the adds which were good and not. They were all about $6.99.

The LED lighted loupe is fine. As well as the flux and tip-tinner.

I found this PIC ammeter at Cool (copied here without permission yet).

I had bought several of the tuxgraphics 3 digit mini-voltmeters which are similar. An AVR instead of a PIC. However it used a sense resistor and voltage divider for the current mode. My setup had so much noise that I gave up for a while. So I ordered an assortment of Hall Effect devices.

The ACS174 is a -30A to +30A sensor out puting a voltage (66mv/A) so it looked perfect. Then while searching for the DIP I discovered it only comes in SOIC. I always wanted an excuse to play with SMT devices. I am hoping it will be noise immune enough to put a couple meters of cable between the sensor and the micro. The sensor needs to be in the boat's engine room and the micro, a more humane environment. Not so much for it, but for me, to read the output.

No tooling here, so here we go again with the markers and scrapers. The chip only needs GND, +5, decoupling cap and filter cap, then signal out. So a simple board.

The same as the first time. I found "Muriatic 29%". Thought I had it figured, but no! I started with 2 cap fulls hydrogen peroxide then one cap muriatic. Nothing after 10 minutes. So I added a little splash of the "Duck" again. Not much more action. I let it sit. Just over an hour and I have holes and low places where the marker was thin but the etch is finally finished.

A few minutes to solder my first SOIC. The web paegs that say "lots of flux and solder, followed by wick" seem to be right on. I just pretended the caps were SMT and put them on top too.

The cable was left over from a failed instrument system. With boat gear, every factory assumes you only install their "1 year warrented system" on new boats, only selling the system with all the wires over each time. This is a 3 wire, shield with drain. Hope it will keep the noise out.

I'm still unsure of the final micro board. This is a mini development board and a USBtinyISP and a display.

I must be on the right track, as after I got the board finished I was surfing to relax and found this from China, only $9. If they could just fix the international world-wide shipping and customs import in some countries, this all might work.

I hope to get some testing in soon. All this web posting uses up the time I could have tested and programmed!

Sitting here wondering where I might find 25 amp of current here in the temporary apartment to test with?

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