how much voltage does picaxe need to be programmed.

ylp88

Senior Member
Normal serial voltages are +/-12V but I think +5/0V should still work as the problem is rarely raised. My friend says that he has a laptop with a 5V serial ouput and his PICAXEs still program successfully.

ylp88

Edited by - ylp88 on 7/18/2005 5:41:17 AM
 

evanh

Senior Member
Yep, no problem, not what RS-232 was spec'd for but no problem all the same. After all, that's exactly how old "serial" mice were able to function without an external power pack.

Usual trick is to use the DTR and/or RTS wires as the power supply. When the comport is opened the software will usually set these lines high (+12 volts). You're out of luck if this does not happen.


Evan
 

hippy

Technical Support
Staff member
I've used a PICAXE powered via serial; diode mix RTS with DTR, and run through a low-dropout 78L05(100mA) to power the PICAXE.

For laptop use, the diode drop and regulator overhead may be a problem, but if RTS and DTR never exceed 6V then the PICAXE can be powered without the regulator - but take care never to plug it into any +12V/-12V serial port ! [ Maybe a 5.V zener across the supply would help ? ]

The big question is, how much current can be drawn from RTS or DTR, and there's no easy answer to that, but it's probably reasonable to say about 10mA per line, 20mA when diode mixed. That's enough to run a PICAXE and even some LED's when 1K8 or 2K2 LED limiting resistors are used ( they are usually still bright enough ).
 

evanh

Senior Member
Heh, just the 5v1 zenor will do the job by itself. It's a bit crude but the line drivers are designed to run short-circuited.

I found a nice selection of data, <A href='http://www.st.com/stonline/books/toc/ds/1341.htm' Target=_Blank>External Web Link</a>


Evan
 
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