LED Popping

[Acetronics2]

I'm after some ideas/tip/tricks to help reduce an audible click when an LED is turned on. .

I actually have two LEDs....an one of the modes has both LEDs flashing alternately - but the clicking is quite bad, so I'm having to rethink!

Hi, Hank

While I was browsing some 18F series Datasheet ( 45K20 abord the PicKit3 demo board ) I found there was some possibility to reduce by soft the slow-rate by a 1:10 ratio when switching the outputs ... see the LATx command chapter.

isn't life marvellous, sometimes ???

Alain

[HankMcSpank]

Hi, Hank

While I was browsing some 18F series Datasheet ( 45K20 abord the PicKit3 demo board ) I found there was some possibility to reduce by soft the slow-rate by a 1:10 ratio when switching the outputs ... see the LATx command chapter.

isn't life marvellous, sometimes ???

Alain

Seems perfect, extract...

10.8 Port Slew Rate Control
The output slew rate of each port is programmable to
select either the standard transition rate or a reduced
transition rate of 0.1 times the standard to minimize
EMI. The reduced transition time is the default slew
rate for all ports.
REGISTER 10-4: SLRCON: SLEW RATE CONTROL REGISTER

Slew rate control register - yippee!! Except I'm using the wrong PIC!

[wanders off cursing. EMI, SHMEEE 'EM I, PICs, Schmics etc]

[Jumper]

Maybe you can use a timer and make a soft pwm (depending of course of the FQ of the pic and if it is busy doing other stuff). Darrel has a SOFTPWM code that might work.

[HenrikOlsson]

Hi,

Slew rate control register - yippee!! Except I'm using the wrong PIC!

And the reduced slew rate would have been selected already since it's the default.... :-(

Have you tried reversing the LED, sinking current into the PIC instead of sourcing it from the PIC, place a capacitor on the 5V rail right next to the LED as well. Not saying it WILL help but it might be worth a shot.

Or if you have more pins free, connect several to the LED, each one with its own series resistor, then turn them from inputs to outputs one after another to "step up" the current - just another thought.

/Henrik.

[HankMcSpank]

Hi,


Have you tried reversing the LED, sinking current into the PIC instead of sourcing it from the PIC, place a capacitor on the 5V rail right next to the LED as well. Not saying it WILL help but it might be worth a shot.

Hi Henrik,

Your suggestion was already going to be on my 'to do' list and do you know what - that sorted it! The switching is in essence completely silent now - even on the guitar amp's highest gain settings.

Actually, in addition to reversing the diodes (to source vs sink current wrt the PIC), I took the anodes of some 'test' LEDs up to my main 8V rail (vs the PIC 4V rail where the LEDs were connected to previously ...ie via the pic internally). The bummer here is I bought 100 x common cathode tri colour LEDS ...now of course, I need common anode tri colour LEDs (which seem very hard to source - one headache solved....another one brewing!). I also boosted the capacitance on the PIC's 4V rail somewhat (wrt this last manoevure - I was just being a tightwad....as tantalums start getting costly once you get above a certain level of capacitance)


Many thanks for all your help - this forum is a great resource.

Hank.