Power Supply Options

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To power the Hummer, you have a two basic options: going through the original battery connections with 5 to 6 volts OR remove the on board voltage regulation components and supply +3.3V.

If there is enough room in your project enclosure for the DTV board, then using the battery connections is probably the preferred method. That method will use approximatley 140mA whereas supplying +3.3V directly will uses about 120mA.

One small problem associated with supplying power through the battery terminal, is the fact that the ON/OFF switch cuts the ground instead of the +V. This will stop a "true" power off condition when other peripherals are attached to the DTV board, such as keyboard and disk drive. In other words, current will still flow through the periphals grounds and keep the DTV from powering down properly.

[edit] Using +BAT and -BAT

Advantages: Simplier to impliment

Disadvantages: Uses slightly more current, larger package, power switch on ground

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[edit] Bypassing on-board voltage regulation

Advantages: Lower current draw, smaller package, power switch on +V

Disadvantes: More complicated, requires cutting of DTV circuit board

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From JTWinters forum post on PETSCII.COM:

http://jledger.proboards19.com/index.cgi?action=display&board=dtvhacking&thread=1170964877&page=1

The entire "power plane" of the underside of the PCB is 3.3v. All I did was find a nice spot where the copper cross-hatching was exposed and I soldered a wire to that. I did the same for the ground on the top plane (check out the images below).

I would highly recommend removing all the original voltage regulation components though. Or you might even go to the extreme like I did and just cut that side of the board off completely.

In my design, I needed 7.5v, 5v and 3.3v. I used a 7805 to step down to 5V. To get the 3.3V, I first tried an LDO but it didn't output enough current. I ended up using a good old LM317 adjustable regulator. I know this solution isn't as sexy as an LDO but it worked.

http://www.picobay.com/picodore64/top%20plane.jpg

http://www.picobay.com/picodore64/bottom%20plane.jpg

Toolbox