Transistor Affecting Timings?

[RossWaddell]

I think I'm already using a 2N2222A - the writing on the casing says, "MPS2222A". I'll try with a 4.7k first and then look into the Darlington configuration (I assume you're talking about two (2) 2N2222A's, right?)

[RossWaddell]

Neither replacing the 10k resistor with a 4.7k nor a darlington pair (your connections didn't work for me; this did, though) helped - after about 1.5 minutes they are out of sync.

[Dave]

Out of SYNC?.....

[Ramius]

Not sure what "out of sync" means either. I doubt the transistors are causing much of a problem and the original idea/suggestion was to ensure that the transistors were driven hard enough to light the LED's. A schmatic/drawing would help if possible. Just an idea, maybe using "HPWM" to set your frequency might help? Perhaps even a combination of "HPWM" and "pause"? Yes I was talking about using 2 transistors. My guess is that you are placing your LED's on the emitter side of the transistors and not the collector?

[Acetronics2]

Hi, Ramius

I see 25 pf as emitter capacitance ... ( see datasheet - Philips p.5 )

Also have a look to the used components for the switching time tests ...

Your comments ???

Now ... your delays are quite long ... could you tell what make you call them " false " ???


But looking at your program closer ... The false delays are obvious - but for some µs only @ each loop ...

do not shoot your transistor, but your program lines ...

Alain

[RossWaddell]

Alain - are you posing your questions to me or to Ramius? This thread was started by me so I don't know what you mean by 'false'. The PAUSEs (approx. 1.5 secs while LED is high, 0.5 secs while low) are the whole point of the circuit - I'm using a PIC to create blinking lights which match an existing model.

Here's the schematic:



Both PICs are programmed with the same code. For about a minute or so after connecting the power, they both blink their LEDs at the same time but slowly get out of sync (one starts flashing before the other) after about 1.5 minutes. Since I'm trying to create EXACT on/off timings, it looks like if I use a transistor (which I need to do as this circuit will light 4 white LEDs) then I have to do this by trial and error rather than relying on the values in the PAUSE command.

[RossWaddell]

Here's a video which shows how the two LEDs start off in sync (first 10s) and then gradually go out of sync (last 10s - clip has been edited for length)