Photovore motors not starting up !!

[neo01124]

I recently made a light follower it worked well on the breadboard(ie the TIP122 was easily driving the motors) but when i put it up on the chassis and soldered everything in place the motors dont turn on  flicking the switch on i.e. if the switch is already on and then i join the connection for motor it runs but when i connect the motor terminals and then switch it on the motors wont run!Seems the motors arent gettin sum sorta pickup? wat is the solution?? all i can think of is using another TIP122 in series with those in place.Thanks already!!

[garriwilson]

Maybe you messed up on your soldering. Like you might have put two solder drops in adjacent holes and they could've fused together.

[Admin]

check to see if anything is overheating (possible short?)

batteries still fully charged?

[neo01124]

yup!! fresh Li ion(LG) batteries in place and in order to avoid a soldering mess up i deliberately used a very large board so every soldered line is at a long distance from the other.Moreover i even tried to test another TIP122 in series with the one already in place and the same problem again!!I dont kno where i'm messin up its the simplest circuit one could make!!

[Admin]

Make sure all your grounds are common (connected). If you get this wrong, sometimes it will work and sometimes not . . .

[neo01124]

i felt the TIP 122's gettin overheated(hot but not really hot) how could that be solved??Moreover what do you mean by common ground,all the gnd connections at one point or all the gnd connections originating from the same ground.If it is the second one then it is already like that.
I have attached my schematic also mayb there might be a more fundamental error which u guys could correct

[Admin]

for reference:
http://www.fairchildsemi.com/ds/TI%2FTIP122.pdf

Your schematic is partially wrong - you are using the transistor properly but not the LDR. In your circuit, the base will always be close to zero volts.

Use the schematic on the photoresistors tutorial:


You just need one more resistor - read the tutorial to calculate the value. Connect Vout to the Base.

what do you mean by common ground,all the gnd connections at one point or all the gnd connections originating from the same ground.

ummmm thats the same thing - as long as they are all connected

i felt the TIP 122's gettin overheated(hot but not really hot)

looking at your schematic, Im surprised its doing anything at all! there is a chance it has been damaged . . . you are in spec, so i guess heatsink it? make the suggested circuit changes and let us know if it works . . .

[neo01124]

what is the reason (theory wise) for keeping base close to zero?? i mean whats the point of another resistor since ldr itself is a resistor?? i shall try it nonetheless

[paulstreats]

The resistor is used for another priniple.

generally, the photo resistor/transistors etc.. detect changes in light and and show these changes up by altering current.

the extra resistor will utilise the special relationship between voltage and current, which is when the current changes, the voltage also must change in line with it(not always present wil ldr type devices)