Author Topic: $40 follower-voltage too high at transistor base  (Read 2385 times)

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Offline agoldTopic starter

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$40 follower-voltage too high at transistor base
« on: March 07, 2010, 03:49:44 AM »
Hi all

I've just finished making the $40 line follower and I'm fairly sure that it's made properly.

However neither motors are turning at all. I first thought that the variable resistors weren't adjusted correctly but I've checked the voltages at the transistor bases and the lowest is 2.15v which I'd assume means that the input to the L293D would always be high (as the transistor turns 'on' at 0.7v according to the tutorial).
Anyone have any idea whats wrong?
Could it be that the LDRs have different resistances in light and dark to the ones in the tutorial so I need to put another resistor in series with them?

Also, what's a good way to tune the variable resistors?

I tried connecting ground straight to the input of the L293D (you could test if the circuit is working like that can't you?) and the motors still didn't move any ideas what could be happening?
How should you debug a circuit like this? that is should you test every single lead to check for shorts and so on or are there better ways?

Thanks for the help,

« Last Edit: March 09, 2010, 04:21:14 AM by agold »


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