A 9 Volt Regulated Power Supply From A 9 Volt AC Adaptor

What I have in mind here is to add an LM317L voltage regulator to the output of a nominal 9 volt AC adaptor to power an Arduino Nano project (a temperature/humidity monitor).

The AC adaptor is a Sanyo model No. 51A-2824. Here's a view of it.

Nominal output voltage is 9 VDC at 100 mA. Measured no load output is about 14.1 VDC. My Arduino device draws about 33 mA, so the AC adaptor's output should be sufficient to cover the LM317L's overhead.

I'm not sure whether this AC adaptor is a linear or a switchmode device. 'Only way to find out is to open up the casing with a hacksaw, so here goes.

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It's linear.

Here's a schematic.

It has a centre-tapped full wave rectifier with a capacitive output filter.

Now to breadboard a regulator.

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And it works. Here's a view of the whole cobbled-together device.

And here's a schematic of my regulator.

Note the following:

• I used a fixed, standard-value resistor (1.5k ohms) for R2. That gave me an output voltage of 9.35V -- plenty close enough for an Arduino's V_IN. For a regulator that's adjustable to exactly 9V, replace R2 with a 2k ohm potentiometer.

Now I have to package the thing on some perf-board, in preparation for doing up a finished, packaged temperature/humidity monitor.

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Perf-Board Module Built -- TUESDAY, MARCH 12, 2019

Here are two views of the module.

Note the use of ty-wraps to secure the transformer and its input and output leads. The unit can be handled without risk of fatiguing and breaking its delicate connections.

And here's the module in its new home, awaiting the build of the temperature/humidity monitor.

'Looks a right mess, eh? So it goes with building electronic prototypes.

Here's a link to the completed temperature/humidity monitor.

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