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having trouble with power supply.


I have used a 40 x2 picaxe IC. My line follower has that,  L7805 voltage regulator , and  the IC L193D motor driver. I`m using 2 300rpm motors and 3 sensors.

My problem is , even though i gave a power supply of 18v, the power is not enough to drive the motors as well as activate the sensors. I can`t use a higher voltage supply because it will burn the picaxe IC.

Help? :S

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L293D *

I've had similar worries with the L293D. That motor driver is made to handle motors with stall current of a 0.6 A and maximum current of 1.2 A even though it might work for a large range of voltage. The reason why both motors and sensors don't work maybe that your motors are made for a higher stall currents and your circuit is not able to provide that. Please provide information on stall currents of your motors. The easiest solution that I can.suggest will be to solder another L293D on top of your current one. That'll double the stall current and maybe your motors will work properly. Also 18 V may be a bit of overkill for the picaxe. I don't have much knowledge on picaxe but while you may supply your micro any voltage in the required range as you please, it'll be better to use something which is just a few volts more than the minimum voltage. I don't know if I'm wrong here though but Ohm's law states that Voltage is directly proportional to the product of current and resistance. Since the parts you are using is decided, resistance is constant. So of you increase your voltage, you decrease the current (for 2 sources having the same power). So if power of a 7 v and 18 v source is same, switch to the 7 v one (again, this deduction us totally theoretical. I don't know how it'll affect it for sure).

a schematic? 18V sounds pretty high to be feeding to a 7805.

yes, 18V uis very high for the picaxe coz a picaxe IC should be ffed a max of 5v. that is why i have used an L7805. it steps down the voltage to 5v.


And i solved the problem. 

i used 2 9v batteries in series because i didnt have a 12v battery. pretty silly mistake to make, i know.

but when i thought about it , it seemed legit logically. series of 2 9v make an 18v. it did not strike me that the current supply would be different. 

and i agree with you vishu. the 300rpm motor needs a lot of current. even while in idle state it does so.

well, i borrowed a 12v and it works now.

thank you btw. :)

Also, i`m thinking of changing the motor driver IC.


replacing the L293D with an L298 !  



a pair of 754410's stacked rather than a 298. I have read about a guy(?) that took 4 754410's, stacked them as 2 pairs, and then wired them together to get about 4A per channel for 2 motors.

Link http://www.starlino.com/motor_driver.html


   9 Volt square batteries are hopeless at delivering current, you might be better off keeping on 9V to power the micro controller through the 7805 and then providing power to the motor drive from 4 AA Batteries, these will give you six volts to the motors, but so much more current than a 9V battery can deliver.

You can see the difference this makes in these two links, the links refer to Arduino and Servos, but the current situtation and solution is the same - 



Duane B.