DPRG mailing list archives: [DPRG] toy H-bridge hacking

Mon Aug 27 11:15:51 CDT 2007

Hmm.... I suppose it wasn't so bad after all.  I guess it's the "fear of
the unknown" (AKA analog) that kept me from attempting it.

I see 2 sets of TO-??? (like a 7805 with heat tab and 3 legs but a little
smaller) with 2 transistors connecting into them through a 1K resistor
from the control chip which says 49.xxxx MHz.

                 _____     _____
                 o  o  o----o  o  o 
                      |               |      
                 o  o  o----o  o  o
                  |                        |
trans   ooo      trans   ooo
              |                         |
           1K                     1K (connect to base of trans?)
             |                          |
 control chip           control chip 

I assume one is forward and one is reverse.  One set is Left and one set
is Right.  So then all I gotta do is cut and connect some sort of
wire/connector to connect to uCU (or back to the original control chip)
and turn on one or the other for forward or reverse and pulse the signals
for speed.

The toy is a 1/16 scale Abrams R/C tank that takes a 9.6V battery pack. 
The turret turns and the cannon cycles up/down.  It has sound, but I'm
not even gonna think about that -- it's way to analog for me.   I really
gotta find that one that shoots the little yellow balls and hook that to
the 1/16 which has LOTS of room in the body (place for main brain and
some sensors) and the turret (place for most of the sensors, their
controller and power supply).

wade

On Sun, 26 Aug 2007 21:51:35 +0100 "Dave Grubb" <davidagrubb at hotmail.com>
writes:
> >I have a few moving toys with H-bridges and I would like to connect 
> up to
> >them and control them with various microprocessors and sensors.
> 
> I wouldn't have thought it would be that difficult. All you need to 
> do is 
> locate the inputs to the H-bridge and test what kind of signals it's 
> 
> receiving. Once you've done that all you need to do is tap the input 
> lines 
> (with a few diodes thrown in if you want to keep the orignal 
> device's 
> functionality) and replicate those signals from the controller. Just 
> lots of 
> experimentation and trial and error really.
> 
> What kind of toys are you refering to? Are you intending to tap the 
> 
> transistors which form the bridge directly or is there some chip in 
> place 
> already which you can use digitally? Many toys I've seen treat 
> H-bridges as 
> digital devices anyway (they only turn the motors on/off, no speed 
> control) 
> and only use +5 or 0v signals (old style Furby comes to mind).
> 
> Dave.
> 
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