I was recommended to use a analog multiplexor to expand the number of
ADC ports on a picaxe "cpu" earlier.
I have now tried to use them for a few days and cant get it working, any
help please
When I connect everything theres light in 2 of the 8 LEDs I used for a
test, even when all 3 pins are low, if I remove the signal wire the 2
LEDs still light.
I connected the 8outputs to a LED each (with an resistor) and the pin3
to a free output pin on the picaxe, and tried directly to +VDC too.
GND to gnd ofcause, and +VDC to +VDC.
I left the E and Vee unconnected, what are they used for anyway ?
What am I doing wrong ?
/Jan
Hi, Jan. I'd guess you're talking about the 74HC4051 mentioned in an
earlier post.
As Mr. Larkin said, the datasheet usually tells all. At least, for
those with a basic electronics background who know where to look.
Since you're a newbie, though, you might want to check the website of
the place where you purchase your ICs. Many have links to the IC
datasheets available on the page where you see the price and
availability.
One source for the HC4051 is On Semi -- here's a link to their
datasheet:
http://www.onsemi.com/pub/Collateral/MC74HC4051A-D.PDF
The 4051 is a curious chip, with an analog section and a digital
section. It's made so you can switch ground-referenced AC signals
that go below GND. To do that, you have to provide a positive and
negative analog voltage which is higher and lower than the maximum and
minimum amplitude of your signal at Vcc and Vee (i.e. +/-5V analog
supply).
However, and I don't believe it directly says this on this datasheet,
if all your input signals are between the digital supply rails (like
your LM35), you can tie Vee to GND and get away without a dual supply.
One thing it does say pretty clearly is that the "E" is an enable, and
it has to be tied low to get it to work. This can be neat if you want
to parallel the single multiplexed pins and, say, make a 24-to-1
analog multiplexer from three 4061s. But if you're just using one
chip, and you don't want to turn the output off, just tie it to GND
and be done with it.
The curious thing is, all datasheets aren't the same. If you look at
the Fairchild datasheet:
http://www.fairchildsemi.com/ds/MM/MM74HC4051.pdf
the information about Vee is specifically mentioned on the first
page. Go figure. In days of yore, I always kept the National Semi
Logic databooks on the shelf for reference. I generally found them to
be the most descriptive. You can now find that set of logic
datasheets at the Fairchild site.
Good luck with your project
Cheers
Chris
