Is there alternative to L293D ?
what make it unacceptable in many lo-voltage application is its minimum supply voltage + output dropoff voltage!
I thought you were a great
I thought you were a great fan of the inverter ICs? they have a super low supply voltage - especially the shmidtt hex inverter? 74c14?
gone back to breadbord and i
gone back to breadbord and i got the issue on breadboard too!
i tought : "wow good, now i can troubleshhot!"
but then at a certain moment it start to work perfectly, and i have changed nothing in the circuit!!!
i am going insane!
the only sure think are:
-it is not a wiring problem. i have checked 20 times
-the problem accurs on the Right motor , no matter which port of the chip i use
so the only thing i can imagine is that the right motor is malfunctioning
BUT if i connect the motor directly to the batttery it rotate at the normal speed and oscilloscope read no strange noise compared to the left one
**Maybe youve tried this**<br><p>Maybe youve tried this already, but heres what Id do..</p><ul><li>Try swapping the left and right motors. Maybe the motor is faulty?</li><li>Test it left and right seperately. One side is interferring with the other?</li><li>Try smaller motors. Perhaps theyre drawing too much current?
how about…
Is there noise jitter in your system?
Edit: Ah wait, I just noticed you’re using a 240…
I wouldn’t actually understand how it might cause the effect you’re seeing, but the those inverters have a bit of hysteresis, so the going high and going low switch voltages are different. At the very least, I would suspect that it could CAUSE one motor to trigger before the other. Can you rewire with a inverter that has no hysteresis?
And the more obvious things like switching motors so left is right, and even switching the ic…?putting a noise-filtering cap over the motor?
I’ve popped quite a few of those 74* ICs…
Possibly brush noise from
Possibly brush noise from motor. Breadboards have a bit of capacitance between connections so offer a little bit of filtering. Try adding some small caps on the motor terminals. 0.1 uF or 0.01 (104 or 103), terminal to terminal initially, then maybe each terminal to motor case if needed.
Definitely looks like some
Definitely looks like some nasty high frequency oscillations going on there. I wouldn’t recommend using the non-Schmitt inverters as the hysteresis helps smooth out any input fluctuations. Unusually high current draw is often a sign that the inverter outputs are being indirectly coupled back to your inputs causing these rapid oscillations, would be read as a ‘forbidden’ logic level by your oscilloscope.
robotologist’s suggestion to try a few filtering caps out is the best place to start, and I would also recommend you try to reduce the amount of loose wiring connected to your inputs. The extra wire acts as a weak inductor/capacitor component, which effectively behaves like an antenna which can pick up noise from the motor windings and output lines, and dump that noise into your sensitive inputs. When your outputs go ‘high’, the signal is bounced back into the inputs, which invert it, causing the outputs to go ‘low’, which is bounced back into the inputs… this cycle can repeat with a frequency in the range of several MHz with 74HC inverters, and often the oscillations won’t stop until you cut power to the chip, or pull out the motor.
Good luck, let us know how it goes =D
The TB6612FNG should be a
The TB6612FNG should be a good replacement for the L293D.
- Motor voltage (VMOT): 4.5 – 13.5 V
- Logic voltage (VCC): 2.7 – 5.5 V
- Output current continuous: 1 A per channel
- MOSFET Driver
Pololu sell this chip on a 0.1" space carrier. http://www.pololu.com/catalog/product/713
tankyou for the helpi have
tankyou for the help
i have tryed all but nothink works
the problem appear and disappear ramdomly (yes on breadboard too)
the only constant is that the problem affect only one of the two motor
the problematic motor produce a strange sound like somethink that make friction (not a smooth sound), but it produce the strange sound even when it works perfectlyt…
anyway now it is korking well i am expecting the next failure…
Inverters as H-Bridges
Hi,
how much current do you need to drive? You are basically using an inverter for its totem pole output, I haven’t checked the 74240 is a totem pole output and not an open collector, although if it works at all my guess is it is totem pole. One thing that does make me a bit nervious is the back EMF depending on the motor, (wireing…) could easily exceed the ratings of the chip, you could be seeing stuck gates because of it.
Have you thought of just building H-Bridges out of FETs/Transistors? This would be the lowest cut off approach basically motor on voltage + 2 diode drops.
all the best
probably discrete h-bridge
probably discrete h-bridge could be the best, but i chose 74 logic for those reason:
-simplicity
-no drop-off
-chip-enable to prive in pwm
anyway could help to place a couple of clamp diode on every motor pin?
discrete h-bridge
I would put clamp diodes on the motor pins, one tied to the +VE rail and the other tied to the -Ve rail, the diode of course orentated so only conduct when the voltage goes over +VE and below -VE.
TTL can fry in funny ways, the back EMF can alos degrade a device rather than distroy it.
yes I was thinking to place
yes I was thinking to place clamp diodes in the way you say…
I forgot to show you the motors:
http://www.robot-italy.com/product_info.php?products_id=1018
my tester reads a current sink of 25mA under "normal" conditions for every motor
from 2 stacked 74AC gates i expect 50ma Max , in fact motors have good torque
I have built a few small
I have built a few small H-Bridges using the Tilden 6 Transistor design, able to control one motor forward and backward ONLY! Be careful because that design has no protection and will have adverse effects if both sides go high, even for a minute. I used these on my EXPLORER robot before i used L298/L293D. I have not had any of these effects from my L293d, but, i’m currently seeking out new power sources or i would test some other configs out.
I’ll look and try to post a the schematics for the Tilden 6 Transistor design h-bridge… pretty simple design actually.