Let's Make Robots!

Md23: the revenge

Hello :) I'm here again to annoy you with my md23 :)

So, a new board has arrived, but now the question is: how do i feed it without possibly burning it ?

I was planning to buy a 12V lead acid battery for the robots, are there some issue i should know? something like the fact that it gives 15V when you least espect it ? :)

Btw, if i would like to use the 12V unregulated adapter, how could i "regulate"  the output?

Also, could i use a PC power supply? It should be switched-mode, right ?

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Check out http://en.wikipedia.org/wiki/Lead-acid_battery

Maybe more info than you care for, but 13.2V is the least amount of "Voltage" you can expect from a fully charged lead-acid battery. However, 15V is out of the question.

You should really read into the use of voltage regulators. Or as Frits would put it: http://letsmakerobots.com/node/88 .

What is true for regulating 7.2V into 5.0V also is true for tuning 13.2V (or more) into 12.0V.


ok, thanks for the info!:)

About voltage regulators: the problem is that they have a drop of voltage.. For example the standard 12V regulator wants between 14,5V and 27V, so a standard 12V battery would not be enought..

I would have thought that a more important consideration when driving motors is the lack of current that regulators tend to output. If you're into a lead acid battery, my guess is you want to draw 1-4 amps. You'll be lucky to get 1amp from a regulator and you'll get lots of heat.

That said: do you REALLY need regulated 12V? Doesn't the MD23 have seperate motor and TTL drive voltages? You could put a 5V regulator in th unregulated line to drive the TTL. The motor drive line shouldn't need to be heavily regulated. This give the bonus that you get more current from your wallwart.

You're assuming too much from me :) i'm just a newbie with too high ambitions :)

Anyway, no the md23 doesn't have separated inputs, it instead have an onboard 5V voltage regulator that it uses for its own logic and as an output for user circuitry.

Reading on the datasheet, it says: "The MD23 is designed to work with a 12v battery. In practical terms, this means the 9v-14v swing of a flat/charging 12v battery is fine. Much below 9v and the under-voltage protection will prevent any drive to the motors. Above 14v and the driver chips may be destroyed - their absolute maximum stress voltage is 18v."

So i think it should work.. Eventually i'll ask my local electronic store if they have a 12V regulated power supply that's cheap enought.. 

I imagine the kit will run fine off the unregulated PSU. Do you know the ripple on the output? Again, though, the problem with the regulated ones is you'll be lucky to find one with a 1A output.