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Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
Do you remember those simple RC cars that went forward when you pressed the button and reversed when you let go? And when they went backwards the car turned. A long time ago I removed all the electronics from one of those cars and they have since disappeared, but I kept the car w/ motor. What I want to do is build a little robot that will drive forward, bump into something and turn while reversing. I am limited to 3 Volts from the two AA's the car can hold. I found the H-Bridge schematic below and it works fine, but I don't know where to go from here. How do I get it to go backwards for a short period of time? If I use a 555 in momostable how do I get complementary outputs?
*Note: I changed the resistors to 3.3K or else it stalls too easily.
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
The easyest way is using a couple of UCCs (37322 and 21) which work well as a motor drivers and that's one of their generic applications as stated in the datasheet. Just connect their inputs together and here you go - a single-wire reversive motor controller (protect it with diodes however). Now add a pull-up resistor after the input pins to connect them to Vcc (or a pull-down to ground, that doesn't matter much) and a capacitor between the pin and the other rail. Add a switch with an antiringing resistor across the capacitor pins and a couple of protective diodes to the input - now whenever the switch (to be rigged to the touch sensor, you can make it either mechanic or electronic, it would be a single NPN or PNP transistor depending on the rail you've chosen earlier in that case) is triggered, the cap will instantly discharge setting the low (or high if you are using a pulldown resistor) input level, and the motor will keep spinning reversed until the resistor charges the capacitor above the threshold voltage.
I'll draw you the schematic later if you want as it's 5am here and I'll have to wake up at 9am ;)
ps this will only work for >4v feed, so for your schematic you'll need two mosfets or an NPN/PNP pair to make the capacitive inputs. Will work quite the same way (connect the gates together and use as UCC inputs in my example), also you can play around with separate gate caps to get some deadtime between motor rotations (will with UCCs as well - just add an RC circuit to each input).
Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
@ LithiumLord: I tried something similar to what you suggested, but with TC4422/1 and it worked, but @ 3V they couldn't move the bot.
I like the Circuits that Anders linked to that use the74HC14, but I wonder if my motor is a little to big for that chip. I have some 74HCT14 and I can't find how much current they can sink/source anywhere. The motor I am using draws ~200 mA no Load to ~1 Amp stalled.
This pdf lists some currents, but I don't know what they mean.
Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
The 74hct14 can't drive my motor, but it can drive the H-Bridge. I have pull down resistor and a capacitor forming an RC time circuit that will reverse the motor when brought up to V+ for a short period of time.
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Small robot question
