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Hi All ,

here is a circuit i have built before and it works very well , but due to a better PCB requirment in my robot project i'll build another one .

before getting into this step i'll upload the schemtic for the current one to hear your comments on it , i know it's not the good design it was my first one.

i need in my new board more safety design to avoid e.m.f.
could you please tell me how to do that.

as for the four optocouplers i have in the current design , 2 of them were burn , in my next PCB design i'll use 2n2222 after those optocouplers....is it right ?

i think the reason is they cannot afford more than 800mA , and i was connecting them to H-Bridge . it was so heavy .

anyway please tell me my mistakes to try to get a better design ,

thank you

as usual i forgot to upload the file

It is hard to follow the schematic, it is too small, so that some of the lines are non visible!

Krumlink said:

It is hard to follow the schematic, it is too small, so that some of the lines are non visible!

Click to expand...

Your mouse cursor should be a little magnifying glass with a + in it. Click on the schematic, and voila! It gets bigger!

oh yeah forgot

or save it on your computer and open it using windows picture display

Hi Watzmann,

just to make sure: Are the outputs of your PIC active high or low? Normally they are active low. In that case your optocouplers are connected inversely.

Additionally I suggest to drive the OCs with an extra low power transistor. That way about 40mA for a safe drive current can be delivered. I doubt that the PIC can stand that load, and it will fry sooner or later (most probably sooner).

A hint to make good schematics: Never route a net wire through an IC. First it looks ugly and second nobody knows where the net is actually connected unless he has the original schematic and can trace the nets using Eagle.

It is also good practice to use flyback diodes on an H switch, as well as a local bulk capacitor.

Boncuk said:

Hi Watzmann,



Additionally I suggest to drive the OCs with an extra low power transistor. That way about 40mA for a safe drive current can be delivered. I doubt that the PIC can stand that load, and it will fry sooner or later (most probably sooner).

Click to expand...

for example i can use 2n2222 , but do you mean to connect it after the optocoupler .

so it will be like that :

PIC signal then Optocoupler then 2n2222 , is it correct ?

no more comments?!