Hi all, new to the forum.
I’m trying to create a circuit supplied by 12v-15v DC. The goal is to get 0.3v-0.8v oscillating around 1hz-1.5hz. I thought I did it with this circuit but after soldering it together it’s clearly flawed. I understand there is supposed to be a 0.7v difference between the emitter and base and that’s probably a good start to solving my problems but I can’t get anything to work in the real world. Any help is very appreciated. Happy holidays!

 

Welcome to AAC!

The goal is to get 0.3v-0.8v oscillating around 1hz-1.5hz.

Where are you taking this output? A 555 timer generates a square wave essentially from ground to the supply voltage.

Any help is very appreciated.

It would help if you labeled the pins on the 555 timer, gave the resistors component designators, and avoided unnecessary wire jogs.

 

it’s clearly flawed

Not clear to me.
How is it flawed?
What are you expecting to see?
Where are you looking?

 

See

 

Thank you for the fast replies! Glad to see this forum is alive and well.

I made revisions on the EveryCircuit app to show what I actually soldered up and circled in red where the app is showing a waveform in purple, which is where I took my readings (pic1).

I used a 9v battery to trouble shoot and make sure I was getting the proper readings. So on the app, when I reduced the supply voltage from 14.7v to ~ 9.47v (actual battery voltage), the circuit still oscillated around .44v to .25v (pic2).
But when I hooked my 9v battery up, I was getting an oscillating voltage from 1v to 1.3v or so.

I looked into it and figured I had the collector and emitter on the transistor backwards. After switching the transistor leads around, I got 0v on the output and 0v at the “collector”.

Before I go and place yet another order on digikey, I want to make sure I’m not grasping for straws again.

Pic3 shows my protoboard as it sits currently with the transistor switched around as stated above.

Pic4 shows the 555 terminals on the app.

I took electronics in college about 8 years ago but clearly I don’t know what I’m doing.

 

See
View attachment 310153

V(tr) oscillates from .8v-0v which should work but is it possible to raise the minV from 0 to .1-.3v?

 

I took electronics in college about 8 years ago but clearly I don’t know what I’m doing.

What is the purpose of Q1?

 

Pic4 shows the 555 terminals on the app.

Could you post the waveform on the threshold pin? I think it should be going to almost 10V, so the peak for the waveform you're showing should be 0.1V lower, not 650mV. The lower voltage should also be higher by almost 5V.

EDIT: Just noticed the resistor you have on the control pin. Will do the calculations when I have time...

 

V(tr) oscillates from .8v-0v which should work but is it possible to raise the minV from 0 to .1-.3v?

 

View attachment 310185

Thank you! That’s awesome! I’m going to try and recreate this on the app

 

V(tr) oscillates from .8v-0v which should work but is it possible to raise the minV from 0 to .1-.3v?

Is the 14.7V power supply voltage required? The last LTspice simulation requires changing Vcc to change the voltage swing.

I think you can achieve this by varying the resistor on the control pin and the 500k in series with the cap. It's an interesting application of the control pin and using a current source to charge the capacitor.

 

ALSO

I realized the EveryCircuit app isn’t always correct because the first circuit I designed allowed me to get the readings I desired when I had a 1M ohm resistor before pins 8 and 4, which made the VCC 0.8v. When I hooked this up and it didn’t work, I looked into it and you need at least 4.5v for most 555 timers to work.

Beware the EveryCircuit app!

 

Beware the EveryCircuit app!

The same applies to all simulators. They can give unrealistic/incorrect results. It's up to the user to sanity check results. In general, I find them a waste of time.

I've simulated circuits in LTspice that LTspice said wouldn't work. I ended up wasting time tweaking components to get the simulation to run. When I breadboarded the circuits, every variation that I thought should work did. I trust the simulator between my ears more than the various programs.

Have you ever heard that saying about monkeys and typewritters?

 

Is the 14.7V power supply voltage required? The last LTspice simulation requires changing Vcc to change the voltage swing.

I think you can achieve this by varying the resistor on the control pin and the 500k in series with the cap. It's an interesting application of the control pin and using a current source to charge the capacitor.

The power supply is a car battery so 12-15v

 

The power supply is a car battery so 12-15v

The circuit suggested in post #9 varies amplitude by varying supply voltage.

I think you'll be better off with your original idea. You can adjust the resistor on the control pin, the resistor in series with the cap, and the charging current.

Since you're going to use this in a car, you should use a voltage regulator and operate at a voltage lower than 12V. Or use a zener diode to make the charging current independent of battery/alternator voltage.

 

The circuit suggested in post #9 varies amplitude by varying supply voltage.

I think you'll be better off with your original idea. You can adjust the resistor on the control pin, the resistor in series with the cap, and the charging current.

Since you're going to use this in a car, you should use a voltage regulator and operate at a voltage lower than 12V. Or use a zener diode to make the charging current independent of battery/alternator voltage.

I like the voltage regulator idea. I found a few options on digikey. Back to the drawing board

 

I like the voltage regulator idea. I found a few options on digikey.

If you use LM317, you don't have to decide on a voltage before you buy. The output voltage is set by 2 resistors.

 

If you use LM317, you don't have to decide on a voltage before you buy. The output voltage is set by 2 resistors.

Currently trying to figure out a way to recreate my original wave form without a transistor and from a regulated lower voltage.

 

I've simulated circuits in LTspice that LTspice said wouldn't work. I ended up wasting time tweaking components to get the simulation to run. When I breadboarded the circuits, every variation that I thought should work did.

Could you give an example of such a circuit, since I've not found that to be true.

 

Didn’t meant to double post…