This one(coral cache) is a bit of a head slapper, but I thought it might come in handy. Laptop (or usb) serial ports are pretty notorious for being stingy on power output. [Roberto] came up with a clever solution. He used a MAX205 (sort of a double+ MAX232) and a singe capacitor to convert the low power serial connection on his laptop to a TTL signal and back again to RS-232. The result is a simple dongle that needs 5v and gives you a high power serial port for those power hungry devices – like [Roberto]’s PIC programmer.
6 thoughts on “Serial Port Power Booster”
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That’s a fantastic idea!
I need one of these for my pic programmer too.
hum the max205 or max203 dont need caps, but it’s cost an arm or a leg for it. It’s just cheaper to get max232 and caps to keep costs low (granted a little more work.)
my “super multi programmer” KILLS my *new* laptops battery i also am in the middle of makeing an extended bat but this is good and i have like 100 max 232s and 1uf caps so im coverd with that
I agree, there’s really not much of a reason to use the max205/203 here. The only reason for Maxim integrating the caps is more to reduce the board space used, and I don’t see this power booster as having portable requirements.
I think calling this a “power booster” is a bit of a misnomer. As I understand, the problem with using portable programmers is not so much the lack of power but the lack of voltage–you need to boost those roughly-ttl level signals from the usb-rs232 adapters to rs232 levels.
I’ve made one of these before with the max232 chip, and the biggest problem I have with them is that you still need an external +5V power source. I think a really great project would be one which draws power off one of the unused RS-232 lines and trickle charges a supercap (you could try a used line, but then you’d have to do something about the ~1F of capacitance slowing down the signals. . .) You might need a boost regulator to charge at ~5.5V and then use a LDO again for the MAX232 chip. I haven’t done the calculations, but I’m pretty sure that a programmer that uses about 20mA + MAX232 (uses
Double plus good, this!
Now all we need is a current limited/fused molex connector for the rear-of-case and we can feed all our amp’ed gadgets. I’ve been toying around with the idea to get rid of those USB power overcurrent/spike issues. Of course someone should make a laptop release as well for the mobile toolkits.