I'm very new to this electronics caper, and have spent the last few weeks learning PICAXE stuff, now I'm trying to do something with it.

All I have to work with at the moment is an 08M, and I'm trying to get the most out of the pins I have.

To this end I've started a project where I'll be feeding fish based on them hitting a lever. But I also want to be able to restrict their intake. The amount and timing of their feeds will be set (probably) with pots at the device. ie away from a computer.

In order to check the settings, I'd like to able to reverse the motor and simulate a days feed, but rather than dump it into the tank, have it come out of the hopper backwards into a bucket.

So I was thinking about using zener diodes.

I know I can do it with another pin on the chip, but this is all about me learning, so I'm trying different things.

Q. is the breakdown reverse voltage aspect of a zener, a thing you can use day, in day out, as reliable property, or is it used more like a fuse or something, that shouldn't be used all the time.


The motor I'll be using is a 36 RPM geared down 12 volt toy motor from Jaycar and I'll only need to run it at say 6 volts to move the fish food for a normal feed.

But I was thinking if I used zenner diodes and another diode after the transistor I might be able trigger the "Simulate a days feed" routine and have that up the voltage to 12 volts, and thus trip the zenner to supply current to the motor backwards.

I hope this makes sense.

I guess the question is....

Q. Is there a way to use zener diodes to reverse the polarity to a motor using nothing but additional voltage, and if so what is that kind of circuit called so I can research it.

Thanks in anticipation

-BullwinkleII

Hmmmm?

You are barking up the wrong tree, there is no hope in hell of a zener diode doing what you want to do.

To reverse the direction of the motor it needs the polarity of the motor to be reversed and this is either done via a H-bridge (or motor drive chip if you have one) or via a DPDT relay, all or each will require additional pins on the picaxe to control.

If its just for testing and setup that you require to run the motor backwards then just swap the wires on the motor manually till you have things working as required then swap the wires back for daily use.

Pete.

ok thanks. I was trying to wrap my head around it, and only got this far...




Not just for calibration testing, I need it to test the feed amount after an adjustment in the field.
I want to make a device that people can use without having to connect to their computer to adjust.

But now that I think of it, perhaps just a jumper to reverse the polarity for those in field tests.

is there such a thing as a switch that has 4 pins that would do the trick?

sorry, just looked up H bridge and all is answered

A H-bridge is really an overkill for this and a simple DPDT (double pole double throw) switch is all that is needed for a simple operational test.

You would wire it like this.



As for setting the motor run time for each lever press, that would be easy by just doing a ADC reading of a pot and using the value for a run period.

This could be done several ways like just taking the motor pin high and pausing for the period of the ADC.

Or do multiple short on off pulses to the motor in a for next loop with the number of pulses controlled by the ADC reading.

Another way would be to use a stepper motor and just advance X number of steps with each step having a amount of food dispensed.
Although using the DC motor and gearbox that you have would work similar to a stepper if driven with short pulse bursts as above.

Pete.

I love it.

Everything I can think of that I need, seems to already exist.

All I need to know is the name.

DPDT switch

Thanks SABorn

Thanks universe

That stuff is all sorted thanks to your (and everybody elses ) help so far.

Thanks again.

Looking at your fish feeded on your site, i would do it a little different and have the bit run through a full section of round PVC pipe, and in the top of the pipe drill a hole so the neck of a 2 ltr coke bottle fitted into the hole, cut the bottom off the bottle and use it for a hopper.
As the bit moved the feed down the pipe more feed would trickle down to replace the feed moved.

This would work in much the same way a grain auger works for filling silos, it would also allow the feed to be covered from moisture and the goat.

I would also use the pulsing method for driving the motor, something like......


for Y = 0 to ADC_count

high motor_pin
pause 10
low motor_pin
pause 10
Next Y


This way you drive the motor with 10Ms bursts and would allow a more consistant form of control

Pete.

Yeah I'm with you on the PVC. The original design only allowed a days worth of feed, so I never built a hopper. I couldnt trust the fish to not overfeed (see Dr. Seuss) so I would only put a day's feed in the system.

PICAXE and electronics changes all that.

We found a new home for the goat (and no, he didn't go to a restaurant/farm, he really did go to a nice family home) so he's not a problem any more


this ...


for Y = 0 to ADC_count

high motor_pin
pause 10
low motor_pin
pause 10
Next Y

I'm not at all familiar with, so I'll have to do yet more study.

I figured I'd be going with PWMout getting input from ReadADC and a pot, but that code looks like some kind of hybrid.

Do I get to save a pin?

That seems to be the driving force in my life. "Do I get to use one less pin?"

Only 4 weeks ago, that was not even on the horizon of concerns in my foreseeable future

See what your help and generosity has done?!

I'm no more crazy than I was before, but it's just a lot more focused now

That's mostly the case with electronics, it's learning what to search for that can take some time. Once you get the right key word (DPDT in this case) you're right.

That's why these forums are so good, there's always someone who knows what will do the job.


I'm not really up on Picaxe code but that will apply N 10mS pulses to drive the motor, where N is based on the value read from the pot.