Help me troubleshoot another circuit?

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kuksul08

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Apparently I suck at building circuits, because they never work for me.

I just built this: http://that.homepage.dk/EVS/

I used all the exact same parts listed there, except at most I had about 11 volts. I checked all the wiring of it, and its right.

Can anyone decipher the circuit and tell me what the voltages at critical points should be? This is frustrating. The LEDs just turn on but don't do anything
 
Measuring voltages won't tell you a lot in this circuit I'm afraid unless you have a CRO and can look at the waveforms.
I know you've probably checked it but are you certain that you have Q1 and 2 the right way around. i.e that you can identify the E,B and C in both the drawing and on the transistor?
If you have a CRO can you see the "pulsing" waveform at the output of IC1?
 
The first thing to do is check that the oscillator is oscillating. Make a probe consisting of a 500 ohm resistor in series with an LED and connect it directly to pin 3 (out) of IC1. It should be flashing or flickering. If it is going too fast to see, try swapping C2 for a larger value like 10 uF or 47 uf until it slows down enough to observe. [Edit: That might be bad advice with that circuit. Increase R1 instead to 500 k or 1 M.]
 
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1 what said:
Measuring voltages won't tell you a lot in this circuit I'm afraid unless you have a CRO and can look at the waveforms.
I know you've probably checked it but are you certain that you have Q1 and 2 the right way around. i.e that you can identify the E,B and C in both the drawing and on the transistor?
If you have a CRO can you see the "pulsing" waveform at the output of IC1?
Click to expand...

hmm.. no, all I have is a DMM. I think Q1 and 2 are oriented properly. I have the R2/R4 junction going into the base, the emitter is grounded, and the collector goes to the LEDs.

One thing that does happen is when I turn the trimmer in R1 to less resistance (200k trimmer and 47k resistor), the LEDs dim the tiniest amount. Thanks so far for the help.
 
Mr Happy said:
The first thing to do is check that the oscillator is oscillating. Make a probe consisting of a 500 ohm resistor in series with an LED and connect it directly to pin 3 (out) of IC1. It should be flashing or flickering. If it is going too fast to see, try swapping C2 for a larger value like 10 uF or 47 uf until it slows down enough to observe. [Edit: That might be bad advice with that circuit. Increase R1 instead to 500 k or 1 M.]
Click to expand...


I did this before the edit - no sign of flickering whatsoever. I will try changing R1 now.
 
OK, with that behaviour adjusting R1 it sounds like your 555 might be oscillating rather than producing a series of pulses. How neat is your layout? (messy layouts can lead to 555's producing oscillations rather than pulses) Do you have a photo?
 
1 what said:
OK, with that behaviour adjusting R1 it sounds like your 555 might be oscillating rather than producing a series of pulses. How neat is your layout? (messy layouts can lead to 555's producing oscillations rather than pulses) Do you have a photo?
Click to expand...
Related to that, pin 5 (control) should normally be bypassed to ground with a small 10 nF capacitor when not used. Also C1 should be connected as closely as possible to the Vcc and Gnd pins.
 
I'm embarrased to show it... this is only the 3rd circuit i've built.
IMG_3961Medium.jpg



Before I bridged most of the connections:
IMG_3962Medium.jpg
 
Those copper pad boards are not very convenient to build with.

Get yourself one of these and build up your circuits bit by bit, testing as you go. While you are experimenting and learning about circuits you don't want to be soldering.
 
I haven't studied the circuit in detail but I think one leg of resistor R1 (the one that is connected to the output of the 555 timer) should be connected to +12 VDC (or +11 VDC in your case) instead of pin 3 of the 555.
 
Mr Happy said:
Those copper pad boards are not very convenient to build with.

Get yourself one of these and build up your circuits bit by bit, testing as you go. While you are experimenting and learning about circuits you don't want to be soldering.
Click to expand...

Yeah it's a pain messing with the soldering. I had thought those breadboards were more expensive. I may pick that one up :)
 
ctom said:
I haven't studied the circuit in detail but I think one leg of resistor R1 (the one that is connected to the output of the 555 timer) should be connected to +12 VDC (or +11 VDC in your case) instead of pin 3 of the 555.
Click to expand...
Actually no, not with that circuit configuration. The output goes high and low and alternately charges and discharges C2 as it goes.
 
Okay, I'm not sure what happened.

I took out R1 and connected power. The LED's were BLINKING for about 2 seconds, then I heard a very slight 'click' and it stopped.
 
Wow...

This is the weirdest thing ever.

So, I took out 47k resistor in R1 right? I still have the trimmer in there. Now, I got a 100k resistor, and touched it to the positive junction at C2, and when I get the other end of the resistor about 1mm from the contact on the trimmer, it starts blinking.

Creepy, but this is good. I think the electricity is going across the small air gap - which means I just need a larger value R1, right?!

edit: If I touch between where R1 is supposed to be, the current goes through my finger. Depending on how hard i press, the frequency changes. haha.
 
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kuksul08 said:
Wow...

This is the weirdest thing ever.

So, I took out 47k resistor in R1 right? I still have the trimmer in there. Now, I got a 100k resistor, and touched it to the positive junction at C2, and when I get the other end of the resistor about 1mm from the contact on the trimmer, it starts blinking.

Creepy, but this is good. I think the electricity is going across the small air gap - which means I just need a larger value R1, right?!
Click to expand...
It is interesting, but it is not really good. I think it means your circuit is being upset by the jumble of link wires and is oscillating uncontrollably.

You may need to take out all the wires and try to make shorter and more direct connections.

As drawn, I think the 555 timer is supposed to be oscillating at ten cycles per second and the decade counter is supposed to be dividing this by ten to produce a one second flash cycle on the LEDs.

So if you left C2 at 470 nF and changed R1 to 1.5 M, or else left R1 at 150 k and changed C2 to 4.7 uF you should be getting a 1 second pulse on the output of IC1 at pin 3. You should check this part of the circuit is working before you connect up IC2.
 
Ok, now I'm both confused and curious...


In the orignial schematic, the output of the 555 time goes high and begins to charge the capacitor C2 through R1. As the voltage across C2 rises and goes above 2/3 VCC, the timer will discharge the capacitor via the discharge pin. Once the output goes low, the R1/C2 circuit is stuck low so I'm confused as to how the circuit could work. I guess I need to study the circuit some more.


kuksul08,

What clicked? Did you smell anything? I had intended for you to connect your potentiometer + resistor combination to Vcc. I don't think 12 volts can jump across a 1 mm air gap so it sort of tells me a control pin on the cmos chip or the 555 is floating. Are you using a 7555 chip?
 
I agree with MrHappy:
"I think it means your circuit is being upset by the jumble of link wires and is oscillating uncontrollably."
Believe me because I've built my fair share of timers that oscillated at unstable high frequencies rather than do what they were supposed to do.
 
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