Powering the motor, motormind B and basic stamp (beginner's question)

Itsenzothebaker

Hello everyone.

I plan to build an automatic whiteboard eraser using basic stamp 2, motormind B and a 24V DC motor. Is there a way to power all three of these devices by using one wall wart?

Thanks in advance,

-Phillip-

Publison

What is the current requirements of the 24 volt motor?

Publison

It will be hard to do it off one wall wart, if you could find one to drive the motor, (I'm guessing 1 AMP +)

The BS2 power input is 5.5 to 15Volt DC, so you will have to regulate the 24 down to say 12 Volt with a 7812 voltage regulator.

Itsenzothebaker

Thanks for the response. Yes, the current requirement is 1.07 amps. So then would I need the voltage regulator again for powering the motor mind b as well?

Publison

Itsenzothebaker wrote: »

Thanks for the response. Yes, the current requirement is 1.07 amps. So then would I need the voltage regulator again for powering the motor mind b as well?

Yes, the Motor Mind runs on 4-7 volts so you would need another 5 or 6 volt regulator after the 12 volt regulator. You could try a 6 volt regulator driven by the 24 volts to drive both the BS2 and Motor Mind, but that would require a fairly large heat sink to dissipate the heat.

IMO, your best bet would be to go with a good, regulated supply such as this, to drive the electronics, and a more robust supply to power the motor. Such as this. It's hard to find a good wall wart worthy of 24 volts. You normally have to look at Laptop Power Supplies like the one I linked to. And by seperating the supplies, you separate some of the electrical noise problems, and brownouts on the BS2.

If you use two supplies, just make sure you have the grounds tied together.

Mike Green

The Motor Mind B requires a power source for the motor (your 24V at over 1A) and a power source for the logic circuitry (+5V at maybe 25mA maximum, typically 5-10mA). Read the datasheet for details.

The Stamp BS2 also requires a power source, either a regulated source of 5V or an unregulated source of 6-9V (maybe as high as 12V, but that's not recommended because of heat dissipation issues). When you provide power to Vin (at 6-9V), the Stamp's Vdd pin can supply as much as 30-40mA at 5V for external circuitry like the Motor Mind B.

If that's all the external load you have to supply, then I'd recommend that you use a 7809 voltage regulator on a heatsink of some sort to supply +9V to the BS2's Vin input using the +24V for the motor. The BS2 will supply the +5V for the Motor Mind B's logic circuitry from its Vdd pin. You'll need a common ground (Vss) for everything with the wall wart wired to the motor, then from the motor to the rest of the circuitry (to avoid ground loops and noise from the motor getting into the rest of the circuitry). Consider putting a 0.1uF 50V ceramic capacitor across the motor windings at the motor itself to help with this.

Itsenzothebaker

Thank you so much Mike and Publison.

Itsenzothebaker

What do you mean by putting the capacitor across the motor windings?

Publison

Itsenzothebaker wrote: »

What do you mean by putting the capacitor across the motor windings?

On DC motor circuits, it is customary to put 1-3 capacitors directly at the motor to reduce the noise from the brushes entering the system.

I always use the three capacitor system.

Here is a tutorial on it:

http://www.beam-wiki.org/wiki/Reducing_Motor_Noise

Here is a picture of what I was referring to:

http://www.harbormodels.com/site08/images/instructions/noise_sup_cap.jpg

I'm not sure if Mike was referring to noise suppression or over all power supply regulation.

Itsenzothebaker

I see. Thank you Publison. I appreciate it.

Itsenzothebaker

I went ahead and purchased the 24v dc converter. How would I connect the wires to the pins? Should I solder the wires to the pins somehow? or A female 6-pin molex?