Im working on a project which cycles through stop,forward, back,left, right modes of a bot using light pulses as input .
light source is laser pointer , room is dark
the circuit is not mounted on the bot, separated by long wire
the circuit -
light pulse -> ldr-> bc337 transistor -> 7404 NOT->4017 decade counter ->7483 full adder -> l293d (10Volt)-> bot
bug - the 7404 inverter out is rising even at falling edge of light pulse
however it works fine with motor supply =6 v and also when dc motor is not connected to l293d
schematic - https://drive.google.com/open?id=0B5m-h82V0Ej2Z0tBb1ZqTE42aHc
is the circuit correct?
any thoughts please help

 

I don't use eagle. Can you post a picture of the schematic?

Did I understand correctly that your problem is that it doesn't work at 10V but does at 6V?

 

I don't use eagle. Can you post a picture of the schematic?

upload file option isnt working
schematic - https://drive.google.com/open?id=0B5m-h82V0Ej2N2kzVWE1UDR0WDg

 

Did I understand correctly that your problem is that it doesn't work at 10V but does at 6V?

yeah you are right

 

High current when the motor runs may be altering the voltage to the ICs, for instance if the ground wire is too small for the current flow. This disrupts the logic signals.

Just speculation, but you did mention a long wire. You may have a large voltage drop.

 

High current when the motor runs may be altering the voltage to the ICs,

entire circuit is mounted on breadboard . l293d driver outputs 1:4 Y connected to bot via long wires.
yeah, multimeter shows 0.4-0.5 v drop over breadboard voltage rail due to high current. how can i fix this?

 

i think the problem is with transistor bc337
due to high current Vee >0v so Vbe changes
so Vout of transistor goes high when it shoudnt
how do i fix this ? if i use 5v voltage regulator 7805 and connect its Vout to 5V voltage rail of breadboard Ill be facing the same problem again.
please help

 

 

Try, as an experiment, using heavy short wires to the bot motors. I'm not sure I understand if the problem is ∆V across the wires or a sagging of the power supply voltage due to the motor load. It sounds like the latter? How about the wires from the power supply to your PCB? Anything carrying the motor current must be capable of that, or allowed to "float" so that a shifting voltage doesn't matter.

 

Try, as an experiment, using heavy short wires to the bot motors. I'm not sure I understand if the problem is ∆V across the wires or a sagging of the power supply voltage due to the motor load. It sounds like the latter? How about the wires from the power supply to your PCB? Anything carrying the motor current must be capable of that, or allowed to "float" so that a shifting voltage doesn't matter.

will replacing the 7404 with a 7414 (Better still, 74HC14) work ??