l293d problem+pic16f877a+dc motors

[binu.kr]

I am making a robot with both automatic and manual control. I am using L293d to drive the dc motor. I am using two 12v dc motors. I am not using a protection circuit (means diode circuit for L293d). It works properly in manual mode. I am using RF transmitter and receiver for manual remote control. Through remote I can also switch to automatic mode. But in automatic mode it just moves and stops while using 12v to 8th pin of L293d. But it moves some more time while using less than 9v to 8th pin of L293d. Can you please help me to solve this problem ?


iam using portc for rf reciever and portd for ir sensor and portb ist 4 pins for l293d ...in automatic mode robot moves a bit and stop and the same time the port b output is in stop condition but in programing i used some delay between forward,right,left and stop but this condition is not satisfied wen i connecting to l 293d and dc motor..if iam check all this things without connecting to l293d ,it works properly pls help me to solve is here any need for uln 2803 for driving portb tol293d
_________________
_________________
nn

[Ttelmah]

First, the 'D' chip, already has protection diodes built in. This is the diffference between it and the older 'B' version.
Difficult to judge what you are doing, since 'eighth pin', means different things according to what package you are using. However 'guessing' that this is the powerdip package, makes this Vs. If so, what _capacitance_ have you got on this pin to the Gnd?. The motor coil flyback, _will_ be routed to this pin. You _must_ have sufficient capacitance here to prevent the supply rail from increasing an unacceptable amount.
Then you have the question of how the 0v connection is routed. You must _not_ have a 'Gnd' connection from the chip to your supply, with the PIC connected somewhere 'along' this wire.
Almost certainly, you are generating supply spikes.

Best Wishes

[binu.kr]

yes you are right iam using PDIP PACKAGE,..Iam not using any capcitors between supply and ground,i dont know abot it please tell me how much capacitance i can use with l293d...can i use 100nf capacitance?
ground is common to all circuits in the board...i think ground is routed correctly and problem might b at not using capacitance .....thaaaaankzzzzzzzzz Ttelmah...many many thaaankzzzzzzzzzzzzzzzz

please give the capacitance value also
_________________
nn

[binu.kr]

thaaankzzzzzzzzzzzzzzzzzzzz Ttelmah ...my circuit working properly i have added .1 micro farad capacitance to vs and vss pins of L293D
AND it working almost properly...so many many thaaa..nkzzzzzzzzzzzzzz
_________________
nn

[binu.kr]

[code]hai Ttelmah
now iam working with a heart beat monitoring project in p16f877a...finger is used to detect the heart beat count....but it doesnt give actual count ..in one minits its counts more than 256...if we not place finger in sensor part its give proper count means '0'..but wen we place the finger between high intensity red led and ldr count is more than 256..i think fluctuations in the finger affecting the sensing part.. i dont know how to attach circuit diagram iam using LM358 and the 7th pin of lm358 is the sensor output ..iam connecting the 7 th pin to a ledand also to PORTC0 PIN BUT IAM NOT USING ANY PULL UP IN PORTCO PIN....CAN U PLAESE HELP ME TO SOLVE THIS PROBLEM
THIS IS THE CIRCUIT DIAGRAM LINK http://onlinetps.com/heartbeat.GIF
THANKZZZZZZZ IN ADVAANZ Ttelmah[/url]
_________________
nn