Enhance Your Plain Vanilla
Supply With A PICAXE
There are several essential tools on any
robotics experimenter bench. From an
electronics standpoint, there are four: a
programmer for the processor of your choice;
a soldering iron; a multimeter; and a
benchtop power supply. The latter is often
substituted with either batteries and/or wall-wart adaptors. However, this is both an
inflexible and unreliable arrangement, and
eventually one finds a need for a "real" power
supply. To do any serious design and
development work, you need a supply with
more features than an on-off switch.
Otherwise, how do you test changes in
performance with voltage fluctuations?
Reliable power is required for work on vision
systems, navigation, IR and US sensors, a
wireless communications link, and more, and
each system typically presents different
power requirements. To get what you need,
you can roll your own, purchase a full fledged
and expensive lab grade unit, or build one of
the many kits found on the Web. Usually, the
end results will be a no-frills unit, with either
fixed or variable voltage, and from one to
three outputs. Voltage and/or current
metering is a big plus, but rapidly becomes
quite expensive. This article presents a cost-effective alternative.
42 SERVO 06.2010
This project is not exclusive to the Elenco kit; it can be used
on any other plain vanilla power supplies, as long as the
following criteria are met:
• Common ground for all the outputs.
• An unregulated DC source around nine to 12 volts. This
usually will be the unregulated source that feeds the +5V
• A maximum of 1.5 amps on the variable outputs; three
amps on the fixed one.
If your supply only has two outputs, you’ll only leave the
unused monitoring channel unconnected.
I originally purchased an Elenco Precision power supply kit
shown in Figure 1. This is a triple output job built around the
ubiquitous LM317/LM337 for the variable voltages and a PNP-enhanced 7805
By Fernando Garcia
for the fixed one.
It all comes in a sturdy and
attractive steel case with all the
necessary hardware, and can be purchased for around $60
US. This is one simple kit, reminiscent of the old EICO kits —
functional but otherwise bare bones — that just begs to be
upgraded. With an upgrade in mind, I designed a board
based on a PICAXE 14M and a few other components which
will add the following features:
• Simultaneous voltage reading of the two variable
voltage outputs and current reading of the fixed
voltage output via an LCD screen. You don’t need to tie
up your multimeter every time you need to make an
• At power-up, the supply starts with all outputs disabled.
When enabling them, they are all enabled
simultaneously — to prevent latch-up in multi-voltage
• Audible alert when enabling/disabling the outputs.
• While the outputs are disabled, they still remain
monitored to allow proper voltage adjustment before
enabling them. This avoids accidentally frying the circuit
with an incorrect voltage.
• Overload current warning via visual and audible alerts.
• Heatsink temperature monitoring which turns on a fan
when a preset temperature is exceeded.