Friday, March 20, 2015

built the ESV

Finally got 'round to building Peter Hiscocks's Expanded Scale Voltmeter for accurately measuring lead acid batteries. Followed the instructions in the October RASC Journal.

Verified I had all the parts (which I had received back in July). Laid out everything on the pre-printed circuit board. At first I was a little confused by some of the resistors. The photograph on page 198 was a little blurry (admittedly, I downloaded the low-rez version of the Oct '14 JRASC) and the colour bands looked different than what I was expecting. But then I pressed further into the article and found the parts table. Ah. Maybe his photo was old, an early version perhaps?

Tested the LEDs. Worked from the centre outward. Soldering went fine. Very well, in fact. Mounted the integrated circuits. Ha! I haven't used that tool for a long time (a chip inserter with pin straightener)!

Careful of the polarity, I connected the new teenie weenie lithium-ion booster battery and tested the circuit. Everything looked OK! Did some calibration but decided to complete it tomorrow by varying the input voltage. The NOCO GB30 was only putting out 11.75 volts! Plugged it in...

Messaged Peter to share the good news. Promised to return all the extra bits and bobs.

Also noted that I thought I found a typographical error...
Adjust the Minimum potentiometer R7 so that pin 4 of the LM3914 is at half the minimum indicated voltage. For example, if the minimum displayed voltage is 11 V, pin 6 should be at 5.5 V.
I believed the reference to pin 6 was incorrect; it should be pin 4. I made that assumption anyway.


Edited on 20 Jan '19 to indicate specific Journal edition.

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