very simple pathfinding robot design help

Thread Starter

calvintennant

Joined Jan 21, 2009
27
Essentially it enables my circuit to use less current?

EDIT:
I am using a phototransistor as my sensor, this way I should be able to push enough current through to lift the base of the transistor, no?
Also, is there a better option as far as a sensor goes?
 

mik3

Joined Feb 4, 2008
4,843
Essentially it enables my circuit to use less current?

EDIT:
I am using a phototransistor as my sensor, this way I should be able to push enough current through to lift the base of the transistor, no?
Also, is there a better option as far as a sensor goes?
What is the maximum current the sensor can handle?
 

mik3

Joined Feb 4, 2008
4,843
Did you replaced T2 with a Darlington one?
Also, you need to place a diode in series with R4 and a diode in series with R5. This is because transistors, even when saturated, drop some voltage across them (across collector and emitter) and this voltage may be enough to partially turn on the other transistor which was supposed to be off. For example, if T3 is on the voltage across it may partially turn on T4 and vice versa.
 

Thread Starter

calvintennant

Joined Jan 21, 2009
27
Did you replaced T2 with a Darlington one?
I'm going to buy a couple extra transistors just in case I need it. I'm going to try to build the robot without it, but in case I need it I'll have it.

diode in series with R4 and a diode in series with R5
Sounds like a good idea, thanks :).

Also, how do I make sure that the transistors I use will be able to handle the current the motors need to run? I've never ordered parts before and I don't want to screw up. :p
 

Thread Starter

calvintennant

Joined Jan 21, 2009
27
Long time, I'm in the process of building this whole thing right now. I've run into a little trouble and I'm falling asleep on my couch trying to get this somewhere.

I am fail at understanding datasheets. Can someone tell me how much current/voltage is needed to turn these transistors on and how much is too much?

NPN Darlington - http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=2SD1275AP-ND
NPN - http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=2SC4953-ND

Thanks all, and night.
 
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