Power From Serial for HC08 (GR8)

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Power From Serial for HC08 (GR8)

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AveryZ
Contributor I
Hi Guys,
 
I am currently powering my setup (GR8, MAX232N, a few sensors) with a USB cable that I hacked in two and pulled the V and G out of. The problem is that now I have this USB cable going into my device, taking up room, and not really doing much of anything except delivering power. What I am thinking is that maybe I can power the device using the serial port in a setup similiar to this:
 
 
So the question is: Could I draw enough power out of the serial port to power the chip and the couple of sensors? (QProx118H, Sharp IR Distance, LM34DZ Temp Sensor (x2))
 
-Avery
 
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AveryZ
Contributor I
Thanks for all your replies! In the end the serial port just didn't have the juice (as was estimated) - I looked into the USB chip but unfortunately they don't have one in a package that I can use (strictly DIP), that would have been pretty awesome though. This is not a production level project so it is OK to just stick with the origional (but ugly) solution which was to grab power from the usb cable and use serial for data in/out - at least we tried :smileyhappy:
 
Thanks,
Avery
 
P.S -> Correct about QProx requiring a seperate voltage regulator - I have this hooked up and everything seems to be working fine (I have no education in EE so I don't know if it is taboo to have a v-regulator hooked up to one random component but not the entire system)
 
P.P.S -> QProx sensors are rediculously cool.

Message Edited by Avery Z on 2007-02-2602:22 PM

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bigmac
Specialist III
Hello Avery,
 
I would even be wary about using 5 volts from the USB port.  The QProx devices have a very tight specification for power supply regulation and noise, to the extent that a separate regulator is recommended just for the QProx component.  Using the supply from a USB port will leave very little headroom, even with a LDO regulator.
 
Regards,
Mac
 
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peg
Senior Contributor IV
Hi Avery,
 
Back in the days when Serial ports in PC,s were implemented on an ISA card you knew what you were dealing with. You could identify the serial driver chips and replace them if you blew it up.
Now that all the serial ports (if you have one) are done in highly integrated port chips on the mother board you usually get less voltage and current from them and if you blow it up you need a new motherboard or try to find a card type one to fix your PC.
So the answer is. Yes, it works but how well depends on the drive capability of the driver involved and whether you can arrange for RTS and DTR to be at logic 0 to share the load.
Perhaps the USB solution is already the best solution??? At least you have a reasonably known quantity here. Although be also wary that virtually none of the "el cheapo" add on devices support the USB2 high speed standard in so far as current output is concerned.
 
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joerg
Contributor II
Hi Avery,
i think today using RS232 is getting sometimes very difficult, since RS232 devices are emulated or attached via USB and this way loosing also the correct timing (IE for programming HC08 devices) or the handshaking does not work (older application with XP!) and so on. So that's why i also suggest to use a USB/SCI converter. The FTDI FT232BM chip (or the newer type with the eeprom incorporated). This way you will get all the benefits from USB without having to bother about the supply current (100mA standard, 500mA max.) the RS232 interface will limit the current to about 10..20mA at 6V (if you have luck 10V).
If you need some schematics let me know.

Saluti Joerg
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