# Best Diode to use



## GOT (Apr 17, 2007)

I have a simple plan to stop my motor without using up a I/O on my prop 2. I will have parallel wires runing to the motor. One wire will have a rocker switch that will break the circuit once the motor reaches a certain point. The other wire will have a diode that will allow me to reverse the direction of the motor, even though the breaker switch is still open. My question is, assuming a 12V DC motor runing on .1 amps, what would be the best diode to use? I've never worked with diodes and the choices are staggering. I could just pick one but I thought I should ask the experts.


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## Dr Morbius (Sep 21, 2004)

I dont think diodes reverse direction, in fact I'm sure of it. Is it conjunction with another circuit? Diodes only allow DC current to flow one way but not the other.


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## GOT (Apr 17, 2007)

I will use a prop 2 signal and a H-bar chip to reverse the direction. I need the diode to stop the flow of electrons to the motor until the prop 2 gives the signal to reverse direction.


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## gmacted (Jan 18, 2006)

It may be very clear to you, but not to anyone else. How about a rough diagram of the setup to make it clearer.


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## GOT (Apr 17, 2007)

Here you go. Hope this makes more sence.


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## The_Caretaker (Mar 6, 2007)

You would be better off using a couple of the inputs on the prop to read the switches and then just control the h-bridge based on which input has been triggered


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## gmacted (Jan 18, 2006)

GOT said:


> Here you go. Hope this makes more sence.


I'm really trying here, but I just can't see it.

Do you have the part number for the h-bridge you are going to be using. If so, post it and I'll look at the spec sheet. I know you're trying to only use one prop-2 output. There may be a better/simpler way. I think you're idea is simple, but I'm just not sure it will work. I need to understand it better before I can make a recommendation.

The other thing that concerns me is the current for the motor. It sounds a bit on the low side. What motor are you using and what type of load (weight) will be on it? Motor current ratings are usually with no load. I'm assuming this platform will have some amount of weight which may cause the motor to draw more current.


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## GOT (Apr 17, 2007)

The motor is allelectronics cat# DCM-274 "Faulhaber 2342.39054. Quiet powerful little DC motor. Operates effectively 3-30 Vdc. 12 Vdc 70 mA no load rating" with a gearhead to make it 120 rpm. The load will be relatively small. I will be using a "Heavy Duty 12VDC 500ma Adapter" from electronics goldmine to power it. For the H-bar, I will either use one of these:

http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-bridge.html

or an L293D chip:

http://www.alliedelec.com/Search/Pr...MPN=L293D&R=2480404&SEARCH=2480404&DESC=L293D

I will try both and see which works best. I know it would be better to use additional ports but I don't got no more ports to use and a precision stop is not an issue here.


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## gmacted (Jan 18, 2006)

GOT said:


> The motor is allelectronics cat# DCM-274 "Faulhaber 2342.39054. Quiet powerful little DC motor. Operates effectively 3-30 Vdc. 12 Vdc 70 mA no load rating" with a gearhead to make it 120 rpm. The load will be relatively small. I will be using a "Heavy Duty 12VDC 500ma Adapter" from electronics goldmine to power it. For the H-bar, I will either use one of these:
> 
> http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-bridge.html
> 
> ...


To be honest, I can see no way to easily use the H-bridge with only one output. I think your best bet would be to use relays and limit switches. Tommahawk provided a circuit here (post #13) that is simple and will work. The normally open contact could be controlled by one output on the prop-2 to make the motor go forward then reverse.

I know you want to use the h-bridge, but you'd have to give me a more detailed drawing of the circuit because the drawing you posted above is too vague and I can't see how it would work. I'm not saying that there isn't a way to get it to work, I just can't see one right now.


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## 4nntt (Nov 28, 2006)

I think your diodes might be backwards in your diagram. Are your switches mechanical? Wouldn't it be easier to use DC and a double-pole switch?


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## pshort (May 6, 2008)

Determine the stall current of the motor so that you can select diodes that will survive if the motor stalls out. If the stall current is under 1A, use a 1N4001 diode (or 1N4002, 1N4003, etc if these are easier for you to get). If the stall current is over 1A and under 3A, use a 1N5400 (or whatever 3A diode you can find at Radio Shack).

As for getting the circuit to work, I think that it will be fine if the output of the Prop is used to control the direction of the H-bridge. It would be best if it was left enabled all of the time. Assuming that the switches are normally closed (except when the motor shaft is at the appropriate limit), the Prop program will raise the output high to drive the motor to one limit (where it stops when the switch at that end opens and stops the current through the motor), and will take the output low to drive the motor to the other limit (where the other limit switch opens to stop the motor again).


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## GOT (Apr 17, 2007)

I will use two ports on the prop 2 - one for the forward and one for the reverse. Forgive me for being simple minded here. My thought process is that there is a forward current passing through the motor that I want to cut with a limit switch (I don't care where that current came from). This switch could be electrical (ie: some sensor that delivers a signal to the prop 2) or mechanical (which causes an open in the circuit and the motor stops). Since I have three different motors with different timings, I don't have room on my prop 2 for one forward, one reverse and one sensor x 3 = 9 ports for the motors. I figure I can save myself 3 ports by using a mechnical switch. The problem with the mechanical switch is that I now have to make the motor reverse direction with an open in the circuit. My simple mind thinks that I can use a diode as shown to allow me to still operate the motor with a reversed current through the diode. I just need to make sure the diode stops the current in the forward direction. I didn't think it would be this involved.


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## pshort (May 6, 2008)

That circuit should work fine for what you've said that you want to do. There is a way to get by with even fewer Prop ports, but that is another topic altogether.

Also, I've noticed that the SN754410 from TI seems to do basically the same thing as the L293 for less money.


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## Dr Morbius (Sep 21, 2004)

pshort said:


> That circuit should work fine for what you've said that you want to do. There is a way to get by with even fewer Prop ports, but that is another topic altogether.
> 
> Also, I've noticed that the SN754410 from TI seems to do basically the same thing as the L293 for less money.


pshort...our GOD of alternate cheaper components!


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## gmacted (Jan 18, 2006)

GOT said:


> Forgive me for being simple minded here.


Don't sell yourself short. You have a great idea. There are just a lot of ways to implement it and that's what makes it complex. What you're thinking may work, but just remember what may be clear in your head, may not be clear to someone else. It's all in the details.

You will get this to work, it just may take some time and trial and error. That's what learning is all about.

Keep plugging away and keep the questions coming. Everyone wants you to succeed, because we all want to see the video when it's done!


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## Koumajutsu (Aug 9, 2006)

Sorry for jumping in so late, but here's the simple answer for you:
Your circuit is *CORRECT*
The best canidate for a diode for you is the *1N4148*.
They're cheap as dirt and you can get them at Radio Shack.
Hope that helps you out


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## pshort (May 6, 2008)

Use the 1N4001 or the 1N5400, they handle far more current than the 1N4148. You can also get them or good substitutes at Radio Shack as well (although maybe not as cheaply as the 1N4148).


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## GOT (Apr 17, 2007)

Thanks guys. I think I've got my answer. This will be my first venture into Prop 1/Prop 2 land. I mentioned them both because I just bought one of each. I think I would be overloading the Prop 2 with everything I want to have happen. If this doesn't work, I can now try the sensor feedback approach. I think this will work, though. Elevator to Hell. Going down....


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