Filtering noises (PIC16F877 and L293D)

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tomas

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Hi, I have one simple question. I need capacitor filters in my schematic to remove noises which are initiated by L293D and RF module, also microcontroller VDD and VSS. Here's schematic I use

This schematic is working (checked in real world), but the problem is with capacitors C3, C4, C13 and C14, when I connect them to the circuit, my programmer does not work. Where I gone wrong? I heard that capacitor filters in schematic with L293D is essential...
 

YOur problem is far from simple and your physical design and choice of power source, wiring, capacitors p/n can either make or break this design.
Please supply photos and parts list for power, and caps.

The L293D is a noise generator which makes high current motor drive current bridge.
The radio cannot be driven using a noise source.
Dont worry about CPU working until you can measure DC voltage on 5V and ripple.

Find out the specs required for running CPU and the radio for DC and AC ripple.

The diode will degrade the 5V regulator however the motors if they reverse or stop quickly can generate a higher voltage which can damage the 5V regulator so different overvoltage protection is needed.
 

My power source for L293D is 6x AA batteries x 1,5 V. For microcontroller its 9V battery. I use ceramic capacitors of 0.1 uF and electrolytic capacitors of 100uF/16V

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now I find out that with ceramic capacitors circuit works fine, but when I add electrolytic capacitors... nothing is working.. So I could soak high-frequancy trash, but what to do with low-frequency trash? How should I remove it if electrolytic caps simply does not work?
 

You will have problems if you drive motor with 2A. maybe your caps were not the right kind or polarity. Vs is a virtual ground near half of supply.. Vss is battery supply which can NOT supply 2A like the L293D may if you are driving motor, you need better power supply.

Anyways you did not report the Vdc of Vs when Caps were installed before. Please do this.

- - - Updated - - -

You will have problems if you drive motor with 2A. maybe your caps were not the right kind or polarity. Vs is a virtual ground near half of supply.. Vss is battery supply which can NOT supply 2A like the L293D may if you are driving motor, you need better power supply.

Anyways you did not report the Vdc of Vs when Caps were installed before. Please do this.
 

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