Diode Switching? Brain freeze.

[Wrenow]

I am having a brain freeze right now - I feel there is a simple solution, it is on the tip of a neuron, but I can't shake it loose.

What I have - a circuit that can run a motor in both directions depending on which servo signal the circuit receives (like a servo or speed controller). So, with a radio control as you move the stick from one end to the other end, it goes to neutral in the middle and then reverses polarity.

What I want - two switched circuits.

I can do this with an 08m, of course, and bypass the circuit entirely, but can I take the existing circuit, and with a diode network of some sort get two different circuits powered depending on the polarity of the input power?

My brain is short circuiting at the moment. Any thoughts?

Cheers,

Wreno

 

[moxhamj]

I sometimes find writing the question as if for someone else then solves the answer. I don't quite understand your question so that may be a reason you can't see the answer. When you say you want two different circuits powered depending on the polarity of input power, is this like a diode bridge? You have 0V on one wire and +12V on the other wire, and one motor runs, and you swap the polarity and the other motor runs? And the motors only run in one direction? The answer to that is to put a diode in series with each motor and wire one so it runs on +/- volts and the other runs on -/+volts. That is two diodes.

But somehow I don't think that is the problem you want solved. That seems too simple.

 

[Wrenow]

Close, but not sure it is a ceegar quite yet. Might actually be that simple - perhaps I am overthinking it. That neuron certainly felt a strong shudder, though - it might just drop into place.

To put a finer point on it the issue. Presume the input is a bidirectional ESC (Electronic Speed Control). The outputs are a couple of solenoids. The higher the speed set on the ESC, the more voltage you have to trip a given solenoid, and, at some throttle setting, the solenoid should trip. When or where in the speed curve is unimportant for the application.

Furthur pondering going on. Surely it can't be THAT easy.....

Thanks,

Wreno

 

[Tom2000]

Close, but not sure it is a ceegar quite yet. Might actually be that simple - perhaps I am overthinking it. That neuron certainly felt a strong shudder, though - it might just drop into place.

To put a finer point on it the issue. Presume the input is a bidirectional ESC (Electronic Speed Control). The outputs are a couple of solenoids. The higher the speed set on the ESC, the more voltage you have to trip a given solenoid, and, at some throttle setting, the solenoid should trip. When or where in the speed curve is unimportant for the application.

Furthur pondering going on. Surely it can't be THAT easy.....

Thanks,

Wreno

Let's see if I can confuse the issue further.

Putting your two questions together, I'm guessing that you're driving a bi-directional motor from a single analog servo channel. You want the single channel to control both the motor's speed and direction.

Center = deadband. Left stick = CCW. Right stick = CW. The more left or right stick, the faster the motor runs.

1. Read and decode the servo pulse from the receiver.

2. Two ouputs from your servo decoder: direction and speed.

Direction might drive a DPDT relay. Speed might be PWM to a MOSFET driver.

Is that what you're after? If not, please post a sketch, showing what you have and what you're trying to do.

Good luck!

Tom

 

[moxhamj]

Your electronic speed control - is this an analog voltage, a pulse width modulation waveform, a pulse position waveform, a 'servo' waveform or some other signal?

 

[Wrenow]

Tom,

Nope, got it a bit sideways. I have an ESC that drives a bidirectional motor in both directions. I want to use it to activate two different solenoids. After ttalking with one of our members who is an engineer today, he confirmed Dr. A's solution. Keep in mind that one does have to deal with the voltage drop issue (well, or MAY have to, depending on several factors).

Thanks, though. And Dr. A - thanks for your solution - I was, indeed, overthinking it.

Oh, and by the way, an example of the ESC is one of the MTroniks range - like the brushed ESC's here http://www.mtroniks.net/mtroniks_SC_products.asp?CategoryID=1&SubCategoryID=3. Takes the servo pulse from the RX, and from that does the magic of supplying a PWM to the motor to control direction and speed. Pretty much the same job as a servo amplifier (the electronics bit in a servo, with the position sensor thwarted) but with much better control over the motor's speed and higher current capacity.


Cheers,

Wreno

 

[gbrusseau]

Wrenow,
Darn, I was convinced this was a contest riddle on your part, and was working on the part where the joystick receiver swings from minus voltage to a plus voltage and that voltage swing had to interface to the ESCs servo control protocol input. I was working out a tunnel diode oscillator to do this, but hadn't worked out the bugs yet. The contest rules where that you couldn't use a PICAXE, but had to use some sort of diode network. Thus the tunnel diode oscillator that varies with the voltage swing, thus producing servo pulses that vary with the voltage swing. Contest rules also stated that it had to be two diode networks. One diode network for the ESC output to the solenoids, and one diode network to convert plus and minus voltage swings to servo pulses. I thought I was adhering to the rules and was close to winning. Extra credit for fooling me.

 

[Wrenow]

Sorry 'bout that. However, in my own defense, I did start out by indicating I was in brain freeze at the time.

Spending the day in special convention electing a new Bishop Suffragan can do that to you. Hey, it only took 6 ballots! Those who know what I am talking about will know what I mean. Those who don't, sorry, long and tedious explanations would be needed - just ignore and move on.

Cheers,

Wreno