[vcf-midatlantic] Apple IIe Voltmeter

[Dave McGuire]

  Very cool, and lots of fun!

           -Dave

On 11/12/2015 11:16 PM, Systems Glitch via vcf-midatlantic wrote:
> VC Forums thread: http://www.vintage-computer.com/vcforum/showthread.php?49958-Big-Voltmeter-The-IMWI-ADALAB-Card-and-an-Apple-IIe&p=389838#post389838
> 
> I discovered my Fluke 8000A no longer measures current (fuse is fine) and realized that meant I had no way to precisely measure current. My other bench meters are analog, lowish impedance, and not precise enough to measure voltage drop across a small-value resistor. Additionally, my Simpson 260 and Simpson 160 meters don't agree on the 100 mA scales -- I believe the Simpson 160 is correct, but needed a way to figure out.
> 
> I thought about using the ADC on a PIC to do the conversion, but my PIC dev stuff is still packed from the move. My Apple IIe isn't though, and I do have an ADC card for it -- the Interactive Microware ADALAB. Someone recently uploaded a manual for it! The IIe also has floating point BASIC, which makes converting ADC to voltage easy with no lookup table, and lets me adjust parameters on the fly -- switching sense resistor values, for example.
> 
> Anyway, I had fun getting the ADALAB tested, and ended up calibrating it with a quick n dirty BASIC program (listing in the VC Forums post) and a LM103 2.7V reference. Good enough to show it works!
> 
> After getting that BASIC extension typed in and making sure it worked, I made extra-sure to SAVE it to disk and avoid having to type it again!
> 
> Thanks,
> Jonathan
> 


-- 
Dave McGuire, AK4HZ
New Kensington, PA