Birdie Posted June 19, 2005 Report Share Posted June 19, 2005 hii 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. Quote Link to comment Share on other sites More sharing options...
Shahriar Posted June 19, 2005 Report Share Posted June 19, 2005 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 Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted June 19, 2005 Report Share Posted June 19, 2005 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 20, 2005 Report Share Posted June 20, 2005 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 20, 2005 Report Share Posted June 20, 2005 Hi Mayooya! ;D Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted June 20, 2005 Report Share Posted June 20, 2005 Good point audioguru, you need a bypass capacitor (about 100nf will do) across the supply, and use a tantelum bead for the 100uf capacitor. Quote Link to comment Share on other sites More sharing options...
Birdie Posted June 20, 2005 Author Report Share Posted June 20, 2005 hey !!!I'm just trying to have all the possible suggestions & solutions. Quote Link to comment Share on other sites More sharing options...
steven Posted June 20, 2005 Report Share Posted June 20, 2005 if you look carefully through the forums youll find a 555 ic timer tester circuit to test the 555 timer Quote Link to comment Share on other sites More sharing options...
sana nasim Posted June 21, 2005 Report Share Posted June 21, 2005 hello every onei 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 Quote Link to comment Share on other sites More sharing options...
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