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Help with transistor switches please!

tranquilityeden

Sep 12, 2012
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Hello All,

I am a brand new member and am desperate for a little help!

I am an absolute noob at electronics but have been given a job by my boss that I need some help with. I have a prebuild, functioning circuit that I want to switch on and off using another circuit. I have been told that this can easily be completed using a transistor as a switch.

I am using a program called Flowol 4 (I am a teacher btw) which is a very basic graphical computer programming package for children that can be combined with a CoCo control box. The result is that using the computer connected to the control box I can turn an output on or off. The output is simply two wires providing 6v. I hope to get this control box's output circuits to control a remote control vehicle. To do this I have opened the remote control unit. The remote control is battery powered and uses rocker switches to make circuits which control the movement of the vehicle. What I want to do is control the vehicle using the remote control but replace the rocker switches with the outputs from the control box.

A friend of mine suggested using a transistor as a switch. I have done a little research but am way out of my depth on this (I am a biologist!). I have been told that using a transistor and some resistors on a PIC board I can make a switch that is turned on when the 6v control box circuit is switched on (vehicle moves forward) and switches off when the 6v control box circuit is switched off (vehicle stops).

I have a RS componants store nearby but have no idea what to ask for. If anyone could tell me which transistor and resistors I need and an idea of how to combine them I would forever grateful!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Ask the physics teacher on staff -- it's probably easier to get help from someone who is easily available.

Aside from that, you've provided insufficient information, and what you have provided does not sound accurate (I would lay bets on the signal from the computer *not* being 6V)

1) Measure the signal
2) determine *how* the switched operate. Do they apply power? Do they pull a logic signal low? Do they pull a logic signal high?
3) what voltages are used in the remote?
 
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KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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So you want to wire some circuitry in to the remote control transmitter so you can make the remote controlled vehicle move and turn, by simulating presses on two centre-OFF rocker switches on the RC transmitter, is that right?

The simplest answer is relays. Reed relays are ideal but any kind will work. Have a look at http://www.digikey.com/product-detail/en/9007-05-01/306-1063-ND/301697

You connect the relay contacts across the contacts in the switch in the remote control transmitter. Your driving circuit has to be able to provide 5VDC at 10 mA or more, into the relay's coil, to activate it. When it does, the relay will simulate the switch being pushed. It's alright to drive a 5V relay with 6V. Polarity is important.

So you would need four relays, assuming there are four actions - forwards, backwards, left and right.

It may be possible to avoid using relays but this would mean investigating the RC transmitter. The simplest and quickest solution is to use relays. The relay contact simulates the switch being activated, and no knowledge of how the RC transmitter detects the switch position is required. It is now possible to activate a switch in two directions at once simultaneously; you should check that this doesn't cause any damage to the RC transmitter.

The relay I recommended has a diode inside the relay to protect the drive circuit against the "back EMF" pulse generated by the relay.

If you tell me where you are, I can look up the relevant RS Components web site.
 

gorgon

Jun 6, 2011
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Based on the very limited technical data on the coco box, I would have used an optocoupler to activate the remote input.

Find the output voltage from the box, compute and use a resistor in series to activate the optocoupler LED with 5-10mA. Observe the polarity of the output. Then connect the output transistor, of the optocoupler, over the input switch of the remote controller. You should measure the polarity of the input terminals so the transistor of the optocoupler is connected correct.

You can use almost any optocoupler for this, due to the low speed of the transfer.

TOK ;)
 
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