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* Dr. Robs First Instalment...
Posted Apr 05, 2003 - 10:48 PM
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A 5 volt regulated power supply for PMR446 using the 12 volt out from a PC power supply. Ideal if you're running a PMR446 gateway and are getting fed up with changing batteries every few hours!

I am using the Binatone as the linked radio and required some sort of external power for the unit as battery life was not so hot.

I came across a piece of technology that has changed the expense and downtime caused by the cells running out at inopportune moments.

The Maplins order code is CH35Q and costs a whapping 33 pence.

It is a 7805 three legged voltage regulator and is a doddle to get going. It requires 12V input - so can be used from either the PC if you are running the eQSO RF Gateway or could also be used in the car for mobile work.

Using 12 volts is also ideal if you're putting the radio some distance from the power source such as in the attic - just put this regulator at the top by the radio and you'll be sure it's getting the full 5 volts. No excuse for voltage drops!

I also purchased some nice black and red colour coded cable a ferrite ring and a pair of dummy batteries to complete the project and recycled an old heatsink from a broken PC PSU.

Stage 1 cut the silver strip of metal in each of the dummy cells roughly in the middle and solder the black lead to the negative end of o­ne of the dummy cells making sure that you fold the other half of the metal strip out of the way. Repeat the process for the red wire to the positive end of the other dummy cell .

Stage 2 cut the cable at the point that you require the regulator to be and attach the two cut black cables to the center pin o­n the regulator. Now attach the red cable that goes to the dummy cell positive terminal to the output of the regulator - double checking that you have the correct pin o­n the regulator.

Stage 3 attach the last red cable to the input of the regulator. At this point feed the output cables through the ferrite ring a few turns - this will help keep the RF out of the power lines. Finally bolt the regulator to a decent heatsink as it does get hot - a light smearing of thermally conductive paste (same as used o­n PC CPU heatsinks) will help the dissipation of heat

This regulator is internally short circuit and thermal overload protected and will shut down when such conditions occur.

Dr. Rob


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