555 Timer problem

[Birdie]

hi
i just wanna ask about something in the 555 timer... i have a school project which is about a digital clock.. i'm attaching a very simplified out line of the circuits.. i'm not attaching the details... anyway the problem is in the 555 timer ...i think it's not working properly so i just wanna know how to check it & to know if it working or not without using the oscilliscope...
Do the values of R1, R2 and C1 make a difference ??? I'm using 10 Kohm & 2.2 Kohm resistors and a 100 micro farad capacitor.
besides is there any way to check counters ???
i hope u can help me.

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[Shahriar]

Dear Birdie

At first disconnect the 555 circuit from your digital circuit, (maybe there is a Short circuit in your digital section).
Then connect the pin 3 of 555 to a usual LED through a 220 ohm resisor. The LED Shpuld blink.
Just Use a normal LED. There are some LEDs that the current they need is around 30mA, So the 555 can not drive them.
555 Can sink current around 15mA.

values of R1, R2 and C1 determine the Freqency and Duty cycle of your output pulse.

HTH - Shahriar

 

[Alun]

Good idea Shahriar, but a normal 555 can source or sink 200mA and the cmos 7555 and courc and sink 100mA, the 555 family is quite tough compared to most ICs. ;D

 

[audioguru2]

The minimum supply voltage for an ordinary 555 is 4.5V with a supply bypass capacitor. An LMC555 Cmos version is guaranteed to work down to a 1.5V supply.
Maybe the 100uF capacitor has a high current leakage. Try another one. ;D

 

[audioguru2]

Hi Mayooya! ;D

 

[Alun]

Good point audioguru, you need a bypass capacitor (about 100nf will do) across the supply, and use a tantelum bead for the 100uf capacitor.

 

[Birdie]

hey !!!
I'm just trying to have all the possible suggestions & solutions.

 

[steven2]

if you look carefully through the forums youll find a 555 ic timer tester circuit to test the 555 timer

 

[sana nasim]

hello every one
i don't know as much as many of good engg r here in this forum but the much i knoe is that the value of resistors  n capacitors depends on the  timing u want to select 4 ur timer wat u r not getting is that first as one of the fellow suggests go through it then connect it to ur digital ckt