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

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

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

Caution: Objects in mirror are more confused than they appear