What's a method of controlling small DC motors by computer?

At only 80 mA per motor you could use transistors. Many signal
transistors will handle this kind of current, though may want to go with
something slighly larger.

But the real issue is the interface and buffer to protect your PC. If
you're not interested in designing and building something yourself, $80
for a relay board is actually pretty good. The relays are more than what
you need, but most commercial products of this nature will err on the
side of larger capacities in order to appeal to a broader group of
users.

-- Gordon

     If you have to ask this question, buy a relay board.  You don't
want to get into the issues of motor brush noise suppression and
keeping inductive kickback out of the PC end of the interface.
With a relay board, there's no electrical connnection between
the switched circuits and the control signals.

                John Nagle

                    John Nagle

Hi Ted,

yes, mechanical relays are quite overkill.

You can replace them with SCRs but your isolation capacities are just
as good as the diode can be, in your case, I do not think that motor
noise will reach the threshold values.

Another way to handle isolation is simply optoelectronic circuits
which insure total indepednance between the power stage to your motors
where you can bring whatever voltage from an external source and the
signal stage to your computer with TTL level voltages either through
your serial link or USB.

Better be safe than sorry,

LHR

On May 11, 8:50 pm, robote...@gmail.com wrote:

Now that's a great idea. Make an H-bridge out of OptoIsolators. Many
optoisolator output transistors can handle 100mA up to 30V. Since the
motors are 80mA and 3V, the optos sound very capable. Some have
differential or totem pole outputs

Looks like with a single HCPL-314J-000E ($2.70) you could do a whole H-
bridge (two logic inputs) for up to 400mA and 30V. Probably need to
add signal diodes for flyback protection, though.

--
Randy M. Dumse
www.newmicros.com
Objects in mirror are more confused than they appear.

Wow! That's an excellent idea.

Many opto-isolators have 100mA capable outputs, some even more, which
well exceeds the 80mA required, Some have totem pole or differential
outputs. Many have output voltage ranges to 30V which well exceeds the
3V required.

A quick look into DigiKey, looks like you could make a complete H-
brdige (two half bridges actually, so it would perform similar to the
754410) with a single HCPL-314J-000E ($2.70). Up to 400mA, upto 30V.

--
Randy M. Dumse
www.newmicros.com
Caution: Objects in mirror are more confused than they appear