555 timer

[things]

i have a kit from jaycar, it's called the jacobs ladder kit, but i can't get the arc to climb the ladder. i feel that the frequency is wrong. i heard somewhere that if you change the resistance between pins 7 and 8, it will change the frequency? also if there are some caps in the 7 and 8 pin circuit, what do they do?
thankyou

 

[bananasiong]

Pin 8 is connected to the +ve supply.
R1 is connected via Vcc to pin 7, you can change the frequency by changing the value of R1. Just refer to the datasheet, it tells you eveything, frequency, duty cycle, etc.

 

[Gayan Soyza]

Seems like its using ASTABLE circuit.

R1 is in between the pin 7 and V+ (pin8)
R2 is in between the pin 7 and pin 2, 6
C is in between the Pins 2, 6 and 0V

If any changes happen to these R1, R2, C the output frequency will be changed.

R1 and R2 is good be in the range 1kOhm to 1MOhm.
If you don’t need a much sensitive Duty Cycle then R1 < R2 so the MARKTIME and SPACETIME are almost equal.

Choose C first or leave it there. Then adjust the R2 or replace R2 with a Variable resistor To get different frequencies.

The exact ASTABLE Frequency can be calculated from the formula given in the data sheet.

 

[things]

what does it mean if there are some capacitors between the pins? here is a pic of the circuit.

 

[bananasiong]

The capacitor at pin 2 & 6 to ground, R1 and R2 determine the oscillation frequency, as mentioned by Gayan. If there is a capacitor from pin 5 to ground, it is used to bypass the noise of the supply. It doesn't affect the oscillation frequency.
Just refer to the datasheet of 555 timer.