Troubleshooting on my first "real" circuit

Thread Starter

christiannielsen

Joined Jun 30, 2019
140
I have on this breadboard a circuit that is suppose to make a servo motor rotate 180 degrees and back again endlessly (for now - later it shall run 5 times and then stop)

fullsizeoutput_39b.jpeg



This is something I put together myself after watching a "hundred" videos so please excuse the mess.

My idea is:
1. The first 555 (ne555) timer is sending a signal to the counter every 1.5 seconds with a duty cycle of 50%.
2. The counter (4017be) sends a signal to the transistor at output 0,2,4,6,8 and 10.
3. The transistor (BC547b) then sends vcc to the discharge pin on the last 555 timer which makes a PWM signal to control the servo motor.
4 When the transistor doesn't send vcc to the discharge pin on the last 555 timer then the discharge draws vcc with higher resistance to change the PWM signal.

And this actually work. BUT only when I pull up the yellow diode on the breadboard!
To see this circuit in action please watch this short video.

My guess is that there is not enough current to the base of the transistor to make current flow through the transistor?
 

djsfantasi

Joined Apr 11, 2010
5,704
Can you post your schematic please? Your picture doesn’t show enough detail to see how it is wired. And it’s near impossible to determine which components and what values you used.
 

BobaMosfet

Joined Jul 1, 2009
839
We are eager to help, but realistically, you need to post a schematic of your circuit- this may seem insignificant, but it's important. Learning to read & write schematics is a critical discipline in electronics and without it, you will never go far. A schematic with all the pertinent information gives us a means to properly evaluate and model your circuit to reproduce your results.

And by the way- great effort on the circuit thus far- that you have something that performs anything without frying, with multiple aspects, is a huge step for you!!!
 

Thread Starter

christiannielsen

Joined Jun 30, 2019
140
Thank you very much for your replies.

I have used a couple of hours in KiCad but unfortunately it got me almost nowhere. To me KiCad is very hard and not that intuitive. And honestly I dont know what to start with when I start drawing the circuit. It will take me weeks to learn how to draw this circuit. But I do understand that you really need it to help with the circuit.

I will browse for another program to draw circuits in.
 

djsfantasi

Joined Apr 11, 2010
5,704
Something as simple as this circuit can be hand drawn. Then take a pic or scan the schematic in and attach the schematic to this post.

Some tips:
Schematics read from left to right. Positive voltage supply is near the top. Ground connections are from the bottom. You can google for Schematic Symbols to see the various symbols you should use. Label each component with a part number and value. Typical part numbers start with specific letters.

  • R - Resistors
  • Q - Transistors
  • D - Diodes
  • C - Capacitors
 

djsfantasi

Joined Apr 11, 2010
5,704
Most of us prefer a schematic instead of a picture of a breadboard.

Here's the relevant portion of your photo:
View attachment 191697
Give the guy a break... It’s been less than three hours since we explained to him how to draw a schematic to post. So far, you’re the fourth person requesting a schematic. I’m not sure, but after the first one or two times, any other request is just annoying.
 

Thread Starter

christiannielsen

Joined Jun 30, 2019
140
Okay so I have drawn a diagram the best I can. I had some trouble with it which I presume you can see but I dont know how to draw it correctly. I think I definitely might have an error around Timer 1.

IMG_1955.JPG
 

dl324

Joined Mar 30, 2015
9,151
Okay so I have drawn a diagram the best I can. I had some trouble with it which I presume you can see but I dont know how to draw it correctly. I think I definitely might have an error around Timer 1.
What you have drawn would be more appropriately referred to as a wiring diagram. A schematic is used to convey circuit intent vs how things are wired.

Without pin function labeled, most would not be able to discern the function of any of the IC's.

I'll draw a schematic and post it shortly.
 

Chris65536

Joined Nov 11, 2019
57
Shouldn't pin 4 of the first 555 be connected to +? It's shown in the drawing, but missing on the breadboard.

MOD:
Merged posts
Both LEDs need current limiting resistors. The lack thereof kept it from working with the yellow LED in place.
 
Last edited by a moderator:

dl324

Joined Mar 30, 2015
9,151
Thank you for using component designators. That will make it easy to discuss the circuit.

Here's what I transcribed:
1574185323735.png
As noted, you're missing some resistors. You should have current limiting resistors for all three LEDs. You're fortunate that CD4017 can't source much current, but I'm surprised that LED1 and LED2 weren't burned out. NE555 can source 200mA.

You're also missing a resistor on the base of Q1.

The wiring on the IC2 doesn't make sense. It's not going to trigger.

The wiring of the control pin on IC1 is also a bit strange. Normally that's bypassed to ground unless you're trying to vary the timing.

R3 shouldn't be necessary, but might be needed to pull up the output of IC1 if you got one that doesn't swing high enough to be considered a logic HIGH for the counter.
 
Last edited:

Thread Starter

christiannielsen

Joined Jun 30, 2019
140
Shouldn't pin 4 of the first 555 be connected to +? It's shown in the drawing, but missing on the breadboard.
Yes you are right. I missed that one. Strange its still working.

I also put in 330 ohm current limiting resistors to the LED's.

After making these changes the circuit unfortunately doesn't do any difference to the matter. I still have to pull out the yellow LED to make the servo run as showed in the video.
 

dl324

Joined Mar 30, 2015
9,151
Af making these changes the circuit unfortunately doesn't do any difference to the matter. I still have to pull out the yellow LED to make the servo run as showed in the video.
Where did you put the current limiting resistor on the yellow LED (LED2 in my schematic)?

The second timer (IC2) still shouldn't trigger. To trigger, the trigger input needs to go below VCC/3 (and it needs to rise above that before the timer times out).
 

Thread Starter

christiannielsen

Joined Jun 30, 2019
140
Thank you for using component designators. That will make it easy to discuss the circuit.

Here's what I transcribed:
View attachment 191930
As noted, you're missing some resistors. You should have current limiting resistors for all three LEDs. You're fortunate that CD4017 can't source much current, but I'm surprised that LED1 and LED2 weren't burned out. NE555 can source 200mA.

You're also missing a resistor on the base of Q1.

The wiring on the IC2 doesn't make sense. It's not going to trigger.

The wiring of the control pin on IC1 is also a bit strange. Normally that's bypassed to ground unless you're trying to vary the timing.

R3 shouldn't be necessary, but might be needed to pull up the output of IC1 if you got one that doesn't swing high enough to be considered a logic HIGH for the counter.
Could you please advice me about the missing resistor on the base of Q1? value and what it does?

IC2 does trigger I would say. It might not be done correctly but it must trigger since the LED is flashing and servo motor is running. Pleas watch the video.

Pin 5 on IC1 does go to ground through the 103 ceramic capacitor. I just didnt know how to draw it.

Thank you very much for spending time on this. I really appreciate it.
 

dl324

Joined Mar 30, 2015
9,151
Could you please advice me about the missing resistor on the base of Q1? value and what it does?
At 5V, the outputs of the 4017 can probably source about a mA. So the smallest value would be around 5k. You could go lower since you don't need the outputs to maintain a valid logic level.
IC2 does trigger I would say. It might not be done correctly but it must trigger since the LED is flashing and servo motor is running. Pleas watch the video.
I missed that you have the second timer wired as an astable. A one shot made more sense, so that's how I read it. What is your intent for the second timer.
Pin 5 on IC1 does go to ground through the 103 ceramic capacitor. I just didnt know how to draw it.
You showed it as being connected between pins 5 and 6.
 

Thread Starter

christiannielsen

Joined Jun 30, 2019
140
Where did you put the current limiting resistor on the yellow LED (LED2 in my schematic)?

The second timer (IC2) still shouldn't trigger. To trigger, the trigger input needs to go below VCC/3 (and it needs to rise above that before the timer times out).
I put the limiting resistor between cathode and ground.

I am unfortunately not strong in practicing VCC/3 and what components it takes to do that. I was aiming for a frequency (I just copied the values of the components from a YT video) to positioning the servo motor at 0 degrees and 180 degrees. I must say though: my multimeter doesn't actually measure what it is suppose to measure :) I dont understand what makes the servo move...
 

dl324

Joined Mar 30, 2015
9,151
I put the limiting resistor between cathode and ground.
Here's an updated schematic:
1574187431247.png
I am unfortunately not strong in practicing VCC/3 and what components it takes to do that.
With VCC=5V, that would be 1.67V.

I was aiming for a frequency (I just copied the values of the components from a YT video) to positioning the servo motor at 0 degrees and 180 degrees.
What does the servo you're driving do? Does it simply drive the motor whenever the timer output is HIGH?
I must say though: my multimeter doesn't actually measure what it is suppose to measure :) I dont understand what makes the servo move...
What are you trying to measure?
 
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