I want to measure low voltage with a PC, cheaply

[Peter Jetson]

I basically want to measure and log battery voltage over a period of
time with a PC. Can anyone suggest some suitable, low cost, hardware
and software?

Thanks, Peter

 

[muzz]

howdy
Ive got one of these
http://www.altronics.com.au/cat.asp?cat=6&grp=39&id=Q1080 works a treat.

 

[budgie]

howdy
Ive got one of these
http://www.altronics.com.au/cat.asp?cat=6&grp=39&id=Q1080 works a treat.

It's a pity that 90% of the el cheapo DMM's don't ever have any
accuracy specs quoted. I was going down that path until I checked for
accuracy. Possibly a better bet - depending on the exact nature of
the BV logging application - is an A/D converter such as:

http://www.kitsrus.com/kits.html#k118

which is also available from Ozitronics (www.ozitronics.com) and was -
a year ago - available from Wiltronics (www.wiltronics.com.au).

 

[Peter Jetson]

Ive got one of these
http://www.altronics.com.au/cat.asp?cat=6&grp=39&id=Q1080 works a treat.

Thanks, but that's rather more than I'd like to spend on this particular
project. If I ever need to replace my multimeter, though, I may look
into such a unit.

Peter

 

[Peter Jetson]

http://www.kitsrus.com/kits.html#k118

which is also available from Ozitronics (www.ozitronics.com) and was -
a year ago - available from Wiltronics (www.wiltronics.com.au).

Perhaps I'm being unrealistic, but $101 sounds a little expensive for a
kit such as this.

Peter

 

[Dave]

Some years ago EA published a project called IIRC 'The Pocket Data
Logger' for exactly this application. Last time I was in Dick Smith
they still had the kit for sale at about $29.95.

I built one at the time of publication & it works well.

HTH

Dave

 

[budgie]

Perhaps I'm being unrealistic, but $101 sounds a little expensive for a
kit such as this.

Maybe you should have a look at the Pico products. That will give you
a guide as to the $ in ready-made units that are sort of comparable.

A lot depends on what sort of accuracy/resolution you want. Most
unspecified cheapo DMM's would be battling to do 0.5% even in their
own minds, while that kit is 12 bit which translates to (1+1 bit)
betetr than .1% plus the MAX chip contribution - far better.

When I was doing a commercial Li-Ion charger design for a client, I
rejected all the RS232-capable DMM's I could find below $100 for
accuracy reasons. I wound up using an HP/Agilent beast with .001% -
that was overkill but it was available at the right price ;-)

At the other end of the scale is the old EA Pocket Sampler kit, which
I believe is still available. 8-bit resolution, which may suffice,
and is HEAPS cheaper than either the K118 or the cheapo RS232 DMM's.

 

[Bob M]

Hi there,

Many ions ago (early 80s), I built a cheap device to measure the 5
volt rail on a computer. I used an 8 bit A>D chip (can't remember
which one at the moment) connected to a UART (used a 6402 UART). The
input to the A>D came from an op amp that had adjustable gain and
offset, set to 30 milivolts per count of the A>D chip. 256 counts
times 30 milivolts equals a range of 0 to 7.65 volts. The 8 bit output
of the A>D was wired directly to the 8 bit input of the UART. A 556
(dual 555) was used to generate the transmitter baud clock and pulsed
the transmitter buffer once a second. The serial output (TTL level)
was connected to a 1488 chip to convert it to RS232 levels.

This resulted in an 8 bit character being sent once a second to the
serial input of the computer that simply recorded the binary voltage
value. A simple program was used to scan the recorded values to see if
any were "out of range" (too high or too low).

Don't know if I can find the circuit, but if you are interested, let
me know and I will try to dig it up. The software used to record/scan
the data would be useless to you as it ran on a DEC PDP 1105 machine.
Used to program in machine code in octal (ah the good old days!).

What voltage range you looking at recording? AC or DC? What resolution
do you require (volts per count)?

Cheers from Canada

Bob Morgoch

 

[David L. Jones]

I basically want to measure and log battery voltage over a period of
time with a PC. Can anyone suggest some suitable, low cost, hardware
and software?

Thanks, Peter

A really cheap way would be to just hook up an integrated ADC chip
(the kind with reference, ranging etc inbuilt) like the Maxim MAX186
onto the parallel port. Shouldn't need much other circuitry around
such a chip. You can get free samples from the Maxim web site too ;-)

A few dozen lines of BASIC or some such programming and you have
yourself a data logger. There is probably some example code and exact
applications for such devices if you have a Google.

A nice multi-channel 12bit ADC chip with precision reference would
make a nitfy precision data logger for almost zero cost.

For an 8 bit solution, I can send you one of these kits for return
postage, think I still have a few kicking around. Won't be able to
send for two weeks until I get back from OS though.
http://www.alternatezone.com/electronics/aiu.htm

Regards
Dave