Hi,

I am going to assist a member of this forum building a can crusher (Electronic projects Designs/Ideas/Reviews --> "Need help with auto starting a motor".

No matter if a can is crushed mechanically or pneumatically, the pressure on it has to be about 70lbs which is also sufficient to completely crush a hand.

To minimize the risk of injuries I want to make a receptacle fitted with a sliding door and driven by a small DC motor with reduction gear.

To activate the crusher an object has to be sensed and the door must be closed.

The door will slide open if an object is brought into sensing range, wait 1 to 2 seconds and then close. This again burries the risk of squeezing fingers in the door, which can be solved for by using an H-bridge IC with current sensing input(s), reversing the motor immediately if something goes wrong.

I have found a lot of H-bridges at ST and National, but not the right thing. They are either half bridges, dual bridges or high power (high voltage) bridges.

Maybe one of you knows a chip which will suit the requirements: single full H-bridge, motor supply voltage 12VDC, continuous motor current 1A, current sensing and several flag outputs (not desperately required) for malfunction tracking.

Remark: Half bridges require power MosFets at the outputs, which is not desireable because of the extra wiring and resulting board size.

Thanks

Hans

Why not just put two button switches in series on either side? Both have to be pressed to activate the crusher. Sorta like missile launches in movies.

Originally Posted by jpanhalt

Why not just put two button switches in series on either side? Both have to be pressed to activate the crusher. Sorta like missile launches in movies.

That comes pretty close to the fully manual muscle operation: Use a timber to crush!

Thanks for the advise.

I will just use TTL compatible logic (5V) for the gates, so the chip won't be a problem to use.

No input will be floating just because active braking is required for both, normal operation and emergency reversing, which applies in any case if the inputs have the same polarity voltage. (L-L = H-H)

If it had an adjustable overcurrent circuit it would be perfect.

Hans


What does serious typo mean?

Hi dknguyen,

I didn't quite understand what should be floating in a circuit with common ground. The reference voltages will be ground and +VS (+12V).

I made a small schematic omitting most of the decoupling measures. Please be so kind as to explain what could be floating in that circuit.

Is the 'SERIOUS TYPO' referred to "lying", "lieing" or to the fact that the picture of yours isn't yours?

If it refers to the words listed, why didn't you post the correct version? You should know that I'm a non-English English. (German)

Hans

Originally Posted by dknguyen

THe high-side transistor will not turn on and stay on properly. It cannot provide a voltage difference between the gate and source that is high enough. It is the voltage across the gate-source that matters, not the voltage between gate-ground (unless the source is connected to ground like it is in the low-side MOSFET).

I'm not worried about that. It applies to every H-bridge though. The chip design should have taken care of that already. Otherwise the chip can be considered to be junk.

Originally Posted by dknguyen

Oh that chip is an H-bridge. NEvermind. I thought it was just a gate driver.

Already forgot it? It was you suggesting the chip.

Free tip: drink more milk!

Regards

Hans

circuit diagram nga po ng h-bridge