When your project is up and
running, you will possibly want to hide it in a hedge to count the number of
birds coming and going from your garden bird feeder, in which case your power
supply will have to be batteries.
However during the development phase, batteries are not ideal, even if
you’re using the rechargeable sort.
The LM2596 DC-DC Step-down
Adjustable Power Supply Module, available from Amazon at £2.99 (postage free
from, I think, China) is also compact, about an inch and a half long, and can
convert input DC voltages in the range 4.5V
to 40V, to 1.5 to 30V (adjustable by the little screw on top of the blue pot)
while being capable of delivering current up to 2A. To mount it on a breadboard, I had to solder
a 7-pin header on to each end.
Then, to display what output
voltage I will it set to, I bought a little digital voltmeter from Adafruit:
And here is the combination
in action:
It is powered by a wall plug adapter
which claims to produce 10V at up to 750 mA.
Here’s where the DMM came in handy – when I checked the DC voltage
produced, I found that the centre pin of the 2.1 mm plug was ground, and the
outer contact was at 9.97 V. This is the
reverse of what I expected, as I have found that more often the inner contact
is the positive one. Interestingly, the
10 V mentioned on the label was not too far out according to my DMM, but often
apparently the quoted voltage can be way off (hopefully the DMM is more reliable). Hence the need to measure, to get at least a
neck of the woods estimate.
In the picture above, the
voltmeter display is connected to the output voltage, and I tweaked the screw
on the blue potentiometer so that it read just under 9 V, in case it was a bit
high for the project I had in mind.
Some devices (chips) operate
at 3.3 V and some at 5 V, and if you apply too much voltage, you can fry your
chips, so all this measuring is really necessary.
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