555 timer vs PIC controller

Thread Starter

drkblog

Joined Oct 4, 2012
109
The transistors are driven by the output of a CD4094 which is 3-state. The easiest would be adding resistor common to all LEDs for sensing the current. But it has to be small.
What are the chances of a hang up in the PIC? The program is going to be quite simple. The PIC is going to be dedicated to the clock signal only.
 

BobTPH

Joined Jun 5, 2013
8,809
That's not the case of this LED. Check figure 1 http://www.farnell.com/datasheets/48181.pdf
Sorry, but that is exactly what the fiigure shows.

At 100mA the output intensity is 1, at 1000mA it is 5, so for 10 times the power you are getting only 5 times the output. Actually is is worse than that because the voltage is also higher at 1000mA, and thus the power is more than 10 times what it is at 100mA. In fact the voltage is nearly double (3V at 1000mA vs 1.6V at 100mA). So, you at 100mA you are using .16W to get 1 unit of light and at 1000mA you are using 3W to get 5 units of light. Or at 100mA you arg getting 6.25 units of light per Watt and at 1000mA you are getting 1.67 units of light per Watt. In other words it is 3.7 times as efficient at 100mA as it is at 1000mA. This is the case for all LEDs that I know of, efficiency decreases with current.

Bob
 

ronv

Joined Nov 12, 2008
3,770
I think I would just make it so it was off when the PIC is in the reset state. Otherwise you could have more failures due to added circuits than the PIC.
 

Thread Starter

drkblog

Joined Oct 4, 2012
109
Sorry, but that is exactly what the fiigure shows.

At 100mA the output intensity is 1, at 1000mA it is 5, so for 10 times the power you are getting only 5 times the output. Actually is is worse than that because the voltage is also higher at 1000mA, and thus the power is more than 10 times what it is at 100mA. In fact the voltage is nearly double (3V at 1000mA vs 1.6V at 100mA). So, you at 100mA you are using .16W to get 1 unit of light and at 1000mA you are using 3W to get 5 units of light. Or at 100mA you arg getting 6.25 units of light per Watt and at 1000mA you are getting 1.67 units of light per Watt. In other words it is 3.7 times as efficient at 100mA as it is at 1000mA. This is the case for all LEDs that I know of, efficiency decreases with current.

Bob
You're right (you were talking about efficiency). But adding 7 LEDs for each output would make the project out of budget. I think I'm going to use two or three LEDs per output. So I can improve efficiency staying within budget.
 

BobTPH

Joined Jun 5, 2013
8,809
Yes, I now understand that you want 8 LEDs for different reasons, I just wanted to correct your assertion that the LEDs were not less efficient at higher currents.

Bob
 

Thread Starter

drkblog

Joined Oct 4, 2012
109
I'm having trouble generating the 38kHz signal with PIC12F629. I'm using timer0 according to this calculator: http://eng-serve.com/pic/pic_timer.html
The PIC is using internal 4MHz oscillator, but I've lost the calibration value for this chip. My code differs in a couple of lines from the code created by the link above, but these lines should be making any difference.

I haven't isolated every possible cause for this problem yet. But maybe someone can tell me if it is possible to do this using the internal oscillator.
 
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