### Author Topic: transistor switching system question  (Read 2203 times)

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#### WaterPig Master

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##### transistor switching system question
« on: November 22, 2008, 02:53:53 PM »
Hi there!

I'm halfway through building my second robot (The first being a very simple line following one) and I need help with the circuit.  The design is a 555 based system where when the tactile sensor on the front is activated, one of the motors reverses for a few seconds.

I have the timing sussed, (after many hours of experimentation), but am stuck over the switching system.  I need a simple circuit, probably using 2 npn or pnps, where when the input is 0, the output is 10 (forwards), and while the input is 1, the output is 01 (reverse).

There is probably a simple solution, and I look forward to hearing it!

Thanks for your help,
WaterPig Master

#### paulstreats

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##### Re: transistor switching system question
« Reply #1 on: November 22, 2008, 03:20:14 PM »
It looks like youre just after logic gates:

http://isweb.redwoods.cc.ca.us/instruct/calderwoodd/diglogic/and.htm This link gives a visual example of how logic gates works

http://hyperphysics.phy-astr.gsu.edu/Hbase/Electronic/trangate.html This link gives transistor circuits for the basic logic gates

#### WaterPig Master

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##### Re: transistor switching system question
« Reply #2 on: November 25, 2008, 01:02:04 PM »
Thanks, I might give that a go.

I think I've found a way to do it completely analog, where you make 2 potential dividers with transistors where one is on constantly, then when the other is activated, that one turns off.  I'm aiming to make completely analog robots, no logic or MCUS at the moment.

All suggestions appreciated though, and if (or when, in my case) the analog system fails, I'll turn to logic!

Thanks,
WaterPig Master

#### paulstreats

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##### Re: transistor switching system question
« Reply #3 on: November 25, 2008, 07:23:50 PM »
(the logic you need is just a simple OR gate).

There are lots of similar type robot citcuits to the one you are building using analog. You just need a comparator. If you had 2 sensors you can even do without that.

Rather than using a tactile switch, why not a infrared emitter/detector pair. They do the same job as the switch except they dont have to make physical contact with a surface to work.

How i would do it is to use 2 infrared emitter/ detector pairs. Put them both on the front of the robot but one to the left and one to the right. If you you wire 1 detector to the motor input for 1 motor and the other to the other motor. When 1 detects a surface, then its corresponding motor will stop leaving the other one running so the robot will effectively turn. (if you made it so the motor reversed when a surface was detected then if both of them detect something the whole thing will back away from it).
In short if you use 2 sensors then you dont need any comparing voltages or logic but you get a more intelligent seeming system.

#### WaterPig Master

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##### Re: transistor switching system question
« Reply #4 on: November 26, 2008, 02:58:19 PM »
Hi there,
Ok, that sounds interesting... I've tried stuff with an IR pair before, and it's never worked.  Don't you need them emitting a frequency so the robot isn't confused by sunlight and remote controls?

Thanks,
WaterPig

#### pomprocker

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##### Re: transistor switching system question
« Reply #5 on: November 26, 2008, 04:07:16 PM »
I need a simple circuit, probably using 2 npn or pnps, where when the input is 0, the output is 10 (forwards), and while the input is 1, the output is 01 (reverse).

First make your truth table

In  Out
A   XY
0   10
1   01

X = A'
Y = A

So all you need is an inverter (Logical NOT)

------|>o------- X
A______|__________ Y

Here is a good tool to help:

http://hopper.unco.edu/KARNAUGH1.1/Function.html

Sorry for my crude ASCII drawing.

http://en.wikipedia.org/wiki/Inverter_(logic_gate)

You can see that the CMOS transistor configuration is the most efficient because one transistors is always off in each state saving battery

« Last Edit: November 26, 2008, 04:17:30 PM by pomprocker »

#### WaterPig Master

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##### Re: transistor switching system question
« Reply #6 on: November 29, 2008, 03:57:20 PM »
Well, thanks guys but I've made a simple system from transistors and resistors.

It uses two voltage dividers, one with the NPN on the +v side, the output of that goes to one motor input and the trigger for the other volt. divider, where the NPN is on the ground side.  I'll post schematics when the 'bot is finished.  It works perfectly!

Thanks for all the help, I'll make logic systems my next project!

Thanks,
WaterPig Master

#### want2learn

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##### Re: transistor switching system question
« Reply #7 on: November 30, 2008, 03:20:08 PM »
The type of robots you are trying to build are great fun
http://tech.groups.yahoo.com/group/beam/
This is the place you need to join, they have loads of schematics and guys willing to help.
Keep looking back here too, Learn this side of robotics too so when the time comes when you want to play about with a horse and rider setup or move onto ucontroller projects you'll be in better stead.
Have a look at the \$50 robot tutorial and contemplate giving this a try later on in your developement.
The question that drives me hazy:

Am I, or the others crazy?

#### WaterPig Master

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##### Re: transistor switching system question
« Reply #8 on: December 02, 2008, 03:01:05 PM »
Hi there

Ah, yes, BEAM robots.  i suppose you could call apple sticker a beam robot...  They're definately something I'm going to try doing seriously (i.e. with solar panels + nervous net) in the future.

I've just re-assembled my switching system on a different place on my breadboard to accommodate the 55 timer... and it doesn't work anymore!  I'll fix it soon enough (hopefully)!

Thanks,
WaterPig Master