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Author Topic: clock circuit problem  (Read 7295 times)

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kam

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Re: clock circuit problem
« Reply #15 on: May 16, 2013, 11:00:33 AM »
"invalid data in file" for all files!  ??? ??? ???

The ground of the uln goes to the ground of your supply. Just make sure that you have a common ground with the LEDs. Do not think the transistor as teh NO contact of a relay! Maybe this is your mistake. The emitter of a transistor switch must have common ground for both the supply of the driver circuit (in your case the input ports of the ULN) and also common ground with the output (in your case the LEDs).

kam

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Re: clock circuit problem
« Reply #16 on: May 16, 2013, 11:02:07 AM »
oh, and please upload schematics with images, the eagle files you uploaded do not work for me

lefteris_

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Re: clock circuit problem
« Reply #17 on: May 18, 2013, 20:46:54 PM »
This is the scematic

I read on the net that i have to use pull down resistors in order to control effectively the led strips with the uln!

kam

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Re: clock circuit problem
« Reply #18 on: May 19, 2013, 17:36:03 PM »
You use 4 2n222 transistors with no resistor base... I wonder how they operate! And i wonder how the PIC is not fried!
So, 2n2222 typical have 40hfe (if i can recall correct), you need say 8x20ma for each digits, say 200mA (always oversize), so the base current must be at least 5mA, PIC voltage is 5v... so use base resistors of 1K for each 2n2222

Next, you need filtering capacitors, one 100uF before the 7805 and one 1uF after. Then you need one 0.1uF as close as possible to the PIC's supply.

The ICL is a nice touch!

I think it will then work.

lefteris_

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Re: clock circuit problem
« Reply #19 on: May 19, 2013, 22:06:15 PM »
I'm sorry,i forgot to mension that the 4 transistors are not 2n222 but c828...  :-[ :-[ :-[

does the filtering has to do with the clock rate(faster than convetional time)?or it is just the parasitic capacitance?

why the pic does not outputs stable signals for each segment?there must be alot of noise.

I will do the filtering capacitors.

Another thing which i say WTF is going on here is that when i connect the signal for the A segment to the pin 1 of the uln and the led's - to pin 16, the led stip turns on with the pin 8, which is the emitter, unconnected...  ???WTF? I think that the circuit got crazy after so many tests...... :o :o

kam

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Re: clock circuit problem
« Reply #20 on: May 20, 2013, 18:21:05 PM »
the filtering capacitors are used to smooth the input voltage and remove spikes and EMI/RFI. You need to use base resistors for the transistors! Check the transistor specifications for the one you use.

As for the ULN, most likely you've fried it big time.