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Require Help with Designing a Circuit for a Project

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jctproject

New Member
Hey guys,

Basically I'm making a project involving a model show jumping fence that can be moved up and down electro-mechanically.

If anyone could help me with designing a circuit for it I would be really grateful. I will show you what I have in mind.


Below is an image of a basic circuit I was intending to use

View attachment 61955



However, in order to operate the motor (and adjust the height of the fence), I would like it to be operated by touch. i.e. have one touch button to move the fence up and another to move it down.

I have another circuit in mind for this below:

View attachment 61956


If someone could tell me how these two circuits could be effectively combined or have any other solutions to move the fence up and down, I would be very grateful.

Thanks :)
 
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leech20e

New Member
If you have a motor that has forward and reverse windings, just use two switches to send power to either the forward winding or reverse winding. Make them momentary 120v or 240v (or whatever voltage the motor is). Just don't press them both at once hehe. That would be easy and simple as long as the operator knows not to use them both at the same time.
 

Reloadron

Well-Known Member
Most Helpful Member
A big part of this will depend on the actual motor used. While the circuits posted will run a motor forward and reverse they are designed around a small single hobby motor. When you say Jumping Fence do you mean as in Equestrian? Should that be the case you are looking at a much, much larger motor and some mechanics.

Ron
 

jctproject

New Member
Sorry, I forgot to mention that this is only for a small scale model. The motor shown in the diagram is similar or the same as the one I intend to use.

Does anyone have any help regarding how to connect the two above circuits together?

Yes, its a model of an equestrian fence

Thanks for your replies
 
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jctproject

New Member
Also, I have the mechanisms sorted...its basically a rack and pinion. Can go into more detail if you wish but the main thing I want to sort out now is the circuit.

Thanks :)
 

alec_t

Well-Known Member
Most Helpful Member
You say you have the mechanism sorted. What current does the motor draw when it is stalled ? That will determine some of the circuit components necessary.
 
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jctproject

New Member
You say you have the mechanism sorted. What current does the motor draw when it is stalled ? That will determine some of the circuit components necessary.
I'm not sure to be honest. What difference does that make to the circuit and the components used??

Thanks for your help, I really appreciate it.
 

alec_t

Well-Known Member
Most Helpful Member
What difference does that make to the circuit and the components used??
The main differences will be the type of transistor necessary and the values of base bias resistors.
Any details you know of re the motor and relay would be useful.
A number of questions:
1) Can you use a multimeter to measure the DC resistance of the motor?
2) What voltage do you plan for the power source?
3) Do you already have a relay for direction switching, or would you prefer to use transistors instead to do that and so save power?
 
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jctproject

New Member
The main differences will be the type of transistor necessary and the values of base bias resistors.
Any details you know of re the motor and relay would be useful.
A number of questions:
1) Can you use a multimeter to measure the DC resistance of the motor?
2) What voltage do you plan for the power source?
3) Do you already have a relay for direction switching, or would you prefer to use transistors instead to do that and so save power?[/QUOTE]

Thanks for your reply.

1) No, I don't think so :/
2) A 9v battery
3) I was considering using a relay to connect the touch circuit to the motor circuit...could you tell me how this could be done?
How would I use transistors to do that and what type would be used??

Thanks again
 
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jctproject

New Member
Would anybody be able to tell/show me how to join the following two circuits together?

I want one touch plate to move the model fence up when finger is placed on it and I want the other to be able to move it down:

http://www.electro-tech-online.com/attachments/

and

http://www.electro-tech-online.com/attachments/


Also, would anyone know if I could use solar power as a power source? What type of solar cells would you recommend and how much would they cost??

I'd appreciate any help, thanks!
 
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alec_t

Well-Known Member
Most Helpful Member
Those are the same circuits you posted originally. It is not helpful to repeat your request!
The two circuits can't simply be joined together; some modification would be needed.
Combining the function of those circuits is possible, but the result is unlikely be satisfactory unless additional circuitry is used, because the relay coil will draw current continuously in either the 'up' or 'down' motor-drive state.
The use of a 9V battery (per post #4), if it's a PP3 type, is not recommended. The motor plus relay current will mean that the battery life is very short. For the same reason small solar cells wouldn't work; you would need decent size ones (which would be expensive).
The BC108 has a 100mA max current rating, so you would need to choose your relay carefully to be well within that if you opt to use a relay instead of transistors for direction-switching.
How would I use transistors to do that and what type would be used??
The transistors would be in an H-bridge configuration. The TIP121 is not ideal for that, because its saturation voltage (Vcesat) is ~1.5V. That means the bridge transistors would drop about 3V, which wastes significant power. There are better and/or cheaper alternatives, particularly if your peak motor current is < 500mA or so. We still have no motor details. Can you tell us at least the motor body dimensions (which would give us a clue about the likely current, hence the most suitable transistors to use)?

From your replies so far I judge you are at the beginner level in electronics (correct me if I'm wrong):). I am concerned that if you are unable to measure motor current you may be unable to find/fix any faults there might be in your circuit when built. Do you have access to a multimeter? Do you understand schematics well enough to produce a circuit layout on Veroboard (strip-board)?
 

jctproject

New Member
Those are the same circuits you posted originally. It is not helpful to repeat your request!
The two circuits can't simply be joined together; some modification would be needed.
Combining the function of those circuits is possible, but the result is unlikely be satisfactory unless additional circuitry is used, because the relay coil will draw current continuously in either the 'up' or 'down' motor-drive state.
The use of a 9V battery (per post #4), if it's a PP3 type, is not recommended. The motor plus relay current will mean that the battery life is very short. For the same reason small solar cells wouldn't work; you would need decent size ones (which would be expensive).
The BC108 has a 100mA max current rating, so you would need to choose your relay carefully to be well within that if you opt to use a relay instead of transistors for direction-switching.
The transistors would be in an H-bridge configuration. The TIP121 is not ideal for that, because its saturation voltage (Vcesat) is ~1.5V. That means the bridge transistors would drop about 3V, which wastes significant power. There are better and/or cheaper alternatives, particularly if your peak motor current is < 500mA or so. We still have no motor details. Can you tell us at least the motor body dimensions (which would give us a clue about the likely current, hence the most suitable transistors to use)?

From your replies so far I judge you are at the beginner level in electronics (correct me if I'm wrong):). I am concerned that if you are unable to measure motor current you may be unable to find/fix any faults there might be in your circuit when built. Do you have access to a multimeter? Do you understand schematics well enough to produce a circuit layout on Veroboard (strip-board)?
Thanks for your reply. Yup, I am @ a beginner level in electronics. The following picture is similar if not the same the motor I am going to use in my project.

View attachment 62014


My motor also has a gear system attached.

I don't have access to a large range of electronics, this is why I was considering a relay. If the circuit will be particularly heavy on power could I just connect a number of 9V batteries in parallel??

I'm not sure if my understanding of schematics will be sufficient. I have designed simple hot and cold sensor circuits on veroboard from circuit diagrams but thats about as advanced as I have got.

I'm sorry I'm making your job to help me so difficult, I really appreciate it however.

I am going to take a picture of the motor and mechanism and I will upload it here in a few minutes.

Thanks again.
 

alec_t

Well-Known Member
Most Helpful Member
I don't have access to a large range of electronics
Where in the world are you? Can you get power MOSFETs?
If the circuit will be particularly heavy on power could I just connect a number of 9V batteries in parallel??
Don't connect PP3's in parallel; use 6 AA (or C) cells in series instead, if you must use 9V. Does the motor have a voltage rating? Or a maker's number we could trace to get data? Perhaps a rechargeable 6V or 12V SLA battery could be used? We're working in the dark here :).
 

jctproject

New Member
Where in the world are you? Can you get power MOSFETs?
Don't connect PP3's in parallel; use 6 AA (or C) cells in series instead, if you must use 9V. Does the motor have a voltage rating? Or a maker's number we could trace to get data? Perhaps a rechargeable 6V or 12V SLA battery could be used? We're working in the dark here :).
I will get the details regarding the motor tomorrow.
Sorry if this sounds stupid but why are the exact specifications of the motor so important??

Also, no I don't think it would be possible for me to get power MOSFETs. I only have a short time to do this so must make use of resources available to me...basic relays, transistors, resistors, capacitors etc.


Thanks for your help :)
 

alec_t

Well-Known Member
Most Helpful Member
My limited research shows some motors that size can take over 1A current, so the TIP121 probably isn't overkill. I was hoping smaller transistors could cope.
Right, here's two versions of a circuit which should do the trick. One has latching touch-switches, the other has non-latching.
Both circuits use a single CD4093 (a quad Schmitt NAND gate IC) to handle the touch switching and provide logic to enable the relay to de-energise (thus prolonging battery life) without the motor immediately running in reverse. Q1 switches the relay; Q2 and Q3 switch the motor. Q2 and the 10k pot provide a variable voltage to the motor. Q3 is any small signal PNP transistor, e.e. 2N3906.
Note that the 4093 has to be a CD4093, to cope with a supply voltage >5V. Being a CMOS circuit it is easily damaged by static electricity, so take anti-static precautions (touch an earthed appliance before handling the IC). I advise using a 14-pin DIP socket to mount the IC.

Edit: DON'T build these circuits. They don't include components for suppressing voltage spikes from relay/motor switch-off. See later post for revised circuits.
 
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alec_t

Well-Known Member
Most Helpful Member
If you feel the above circuits are too complex for your building skills then here's a much simpler one. Your post #1 circuit has only one switch, but you wanted separate 'up' and 'down' switches. To keep things simple and cheap, these are best implemented with button-operated SPDT change-over microswitches rather than touch switches. The switches need to be rated at at least 1A DC. This new circuit also includes two diodes which effectively disconnect the pot when neither switch is pressed, to avoid current drain when the circuit is not in use, and so eliminate an 'off' switch.
 
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