Output voltage

wrangler1120

Is the microcontroler limited to only +5V output or is it possible to get more, say 12V. I need to power a motor which operates at 12V. Just wondering if I'm going to need to devise a circuit to take the output from the stamp and "convert" it to 12V.

Philip Gamblin

Do Not try to power a motor directly from a Stamp pin. Use the stamp to drive a transistor which will in turn drive a relay·or motor.

LoopyByteloose

You need to have a device which will bring the voltage up to 12 volts.
And you need a 2nd source for the 12 volt power

First, you need to figure out how much power that 12 motor might use. Power = Watts = AmpsXVolts.

Since you only have the Volts, you need to estimate the AMPs. This can be done indirectly by measuring the resistant in the motor.

Lets say that you measure the motor with a Multimeter and it reads 40 ohms. Using Ohm's law E=IXR, you can plug in two number 12= I x 4 and find out that the motor takes roughly 0.333 amps or 333 milliamps [noparse][[/noparse]way too much for the BasicStamp's limited output of roughly 25ma @ 5 volts.

The motor's power is 12 volts X .333 amps = 4 watts. So you need a Transistor of some kind that will handle 4 watts or more. It is best to get some room for error. So a 10watt MOSfet would probably be very safe.
And if you buy a MOSfet that is rated at 20 or more volts, it will still work too.

A ULN2308 won't work because it is limited to 0.500 watts for the whole device. It will burn up. {just like that Stamp which is limited to .125watts per pin [noparse][[/noparse] .025ma x 5] and I suspect some other limit for all the pins being on at the same time.

Try searching this site for MOSfet and you will come up with some schematics and how to connect safely with the Stamp.

Okay?

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······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

allanlane5

The BS2 is a 5-volt device. However, it can control OTHER devices (like a MOSFET, or a Relay, or a Darlington Array like the ULN2308) which can switch current at higher voltages for motors and the like.

That's what Kramer is referring to above. There are excellent Nuts&Volts references on the Parallax web site, you might check them out: http://www.parallax.com/html_pages/downloads/nvcolumns/Nuts_Volts_Downloads_V2.asp

wrangler1120

Yeah I figured it out. I used half an H bridge since I did not need to reverse my motor. Everything works fine, and we hope to implement the design/prototype in my parter's car.

Thanks guys