Timing the 555 chip for the Enterprise?

[MillenniumFalsehood]

Okay, I like simplicity, and you don't get much simpler than the 555 chip. So, does anyone know offhand what the correct resistor values are for the blink rates on the Enterprise Refit? Alternatively, is there a formula that I can plug a blink rate into and find the resistor value?

[Pat Amaral]

I don't have the timing values for you but I recommend you do what I do. Breadboard the circuit, replacing the timing resister with a potentiometer. You'll also need to get a few various value capacitors to swap out because you'll want to vary the flash duration (the time the LED is actually on).

Once you have everything hooked up, adust the resistance and cap values until you have the rates that look good for your application. Then just measure the pot's value with an ohm meter and replace the pot with the closest restister you can find.

easy peasy

[tetsujin]

Depends on how you define "simple", I guess...

Having a dirt-cheap 8-pin analog IC with external capacitors and resistors driving a total of one blinker is "stone knives and bearskins" simple...

Having an almost equally cheap 8-pin digital IC which requires no additional external components (apart from current-limiting resistors, maybe) to drive up to six blinkers is "easy to manage" simple - if you're down with coding at least...

But to talk 555's - the timing of the 555 is controlled by the charging rate of the external cap - the voltage across the cap is compared to values generated by a resistor network that acts as a voltage divider.

Check this site

In "astable mode" the cap charges up to 2/3 of V and then discharges to 1/3 of V and repeats - the time for the charge/discharge depends on the values of the two resistors:

t1 = .693(R1+R2)C
t2 = .693 x R2 x C

t1 is the time the light is on during each pulse, as the cap charges
t2 is the time the light is off during each pulse, as the cap discharges.

So choose your values of C, R1 and R2 and you can get the frequency and duty cycle you want...

[USS Atlantis]

Depends on how you define "simple", I guess...

Having a dirt-cheap 8-pin analog IC with external capacitors and resistors driving a total of one blinker is "stone knives and bearskins" simple...

Having an almost equally cheap 8-pin digital IC which requires no additional external components (apart from current-limiting resistors, maybe) to drive up to six blinkers is "easy to manage" simple - if you're down with coding at least...

But to talk 555's - the timing of the 555 is controlled by the charging rate of the external cap - the voltage across the cap is compared to values generated by a resistor network that acts as a voltage divider.

Check this site

In "astable mode" the cap charges up to 2/3 of V and then discharges to 1/3 of V and repeats - the time for the charge/discharge depends on the values of the two resistors:

t1 = .693(R1+R2)C
t2 = .693 x R2 x C

t1 is the time the light is on during each pulse, as the cap charges
t2 is the time the light is off during each pulse, as the cap discharges.

So choose your values of C, R1 and R2 and you can get the frequency and duty cycle you want...

Also remember that under normal circumstances, the 'duty cycle' - I.E. the time the light is on - is normally at least 50% - meaning you can't have a 1/10 second on, 9/10 second off cycle

You can get around this by putting a standard 1N4148 signal diode across R2 - what this basically does is invert the cycle

A basic schematic is Here with a mini-movie of how that design works Here