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Topic: First project - help with code and vibration motor (Read 1 time) previous topic - next topic

ReverseEMF

#15
Apr 14, 2018, 08:51 am Last Edit: Apr 14, 2018, 08:58 am by ReverseEMF
Yes, I'm really struggling with that. It's marked bc337 but I've seen that unit used for other purposes with different pins. It's also too fiddly. I've just ordered some TIP120 replacements that seem clearer
A TIP120 is not a good choice for this application.  It's a Darlington transistor and thus has a very high VCE(sat). What's that, you say?  Very simple - it's the voltage from the Collector to the Emitter when the transistor is turned "on".  And for a darlington, that can be 1.4V or more -- hard to say what it will actually be in this case, since the TIP120 transistor isn't meant to be used at such a low collector current and with such a low voltage.  After the Collector-Emitter junction (or "path") drops it's voltage (something like 1.4V), there won't be much left for the motor.

Really, the best bet would be to use an N-channel MOSFET, or a TIP31C.  If you use the TIP31C, then put a 220Ω resistor on the base.  That will allow around 20mA on the base, for a good 0.4V to 0.5V VCE(sat), all the way up to 2A at the Collector.  And, if it turns out you need a little more head-room on the Collector side (i.e. the motor still isn't running properly), then try a 120Ω ¼W resistor on the base, for Collector current up to 3.5A. 

A good MOSFET would be: STP16NF06L p/n 2001373 at Jameco.  It's a cheap Logic Level N-channel device with plenty of headroom, and with a channel "on" resistance of only 0.1Ω worst case, any voltage drop across the Source-Drain will be negligible.

And, BTW: I'm not sure what you mean by "too fiddly".
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ReverseEMF

Yes. I've 330 and 220. Where would I put the power onto the circuit so that the output 3 still controls the transistor?
Connect the Collector (on the transistor) to the minus lead on the motor, and the positive lead, of the motor, goes to some external source, like the positive side of two or three AA cells in series (as advised by slipstick).  And, of course, the negative side of the battery (i.e. the 2 or three AA's in series) goes to the Emitter (on the transistor).
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Please DON'T PM me regarding what should be part of the Public Conversation -- Let it ALL hang out!!
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