Trouble: Simulator expectations vs constructed circuit; 555timer.

Thread Starter

Genosphere

Joined Dec 8, 2020
7
So I am having some trouble building the circuit I had built in a sim, several to be exact, which all seemed to work the way I wanted them to. Now that I have built the circuit on a board, Im not getting the results expected. Checked wiring and and parts, things look ok. Odds are I have missed something in calculations and just not seeing it.

The goal is to power a little MP3 player that connected to the other side of an optocoupler, the optocoupler in this case is replaced by an LED on the right in the drawing below since it wasn't offered in the software; seeing as the side im connecting to is basically an IR led i believe I should be ok.

The device(LED) should be on for about 3-4 seconds t=(1.1*RC){R=330k and C=10uF}, then off.

Could anyone please check and see if i may have missed something in calculations or configuration?

Link to sim: https://everycircuit.com/circuit/6394445589905408

Diagram: projectv2.png
 

Thread Starter

Genosphere

Joined Dec 8, 2020
7
I think I forgot to save it as public: https://everycircuit.com/circuit/6394445589905408

So, I must either AC couple the trigger with a negative pules or short it to to at least 1/3 of Vs?

Can I do this by using a PNP+NPN setup?
Originally I thought this would work(below is the schematic): https://everycircuit.com/circuit/4668020545552384
npn_pnp_555_switch.png
I don't think it really made sense with the PNP seeming redundant.

Any suggestions on how to trigger the switch without using an AC signal? The circuit is to be installed on a vehicle so It really only sees DCV. I was trying to stay away from mechanical relays to keep things small.

~~~~~~~~~~

Either way, this has taught me a lot so far, got to build my first PCB and was pretty cool to see my own circuit board come to life like my CAD designs and 3D printing, even if it failed the first time. lol

Keep the good info coming and thanks so far,
Geno
 

eetech00

Joined Jun 8, 2013
2,376
So I am having some trouble building the circuit I had built in a sim, several to be exact, which all seemed to work the way I wanted them to. Now that I have built the circuit on a board, Im not getting the results expected. Checked wiring and and parts, things look ok. Odds are I have missed something in calculations and just not seeing it.

The goal is to power a little MP3 player that connected to the other side of an optocoupler, the optocoupler in this case is replaced by an LED on the right in the drawing below since it wasn't offered in the software; seeing as the side im connecting to is basically an IR led i believe I should be ok.

The device(LED) should be on for about 3-4 seconds t=(1.1*RC){R=330k and C=10uF}, then off.

Could anyone please check and see if i may have missed something in calculations or configuration?

Link to sim: https://everycircuit.com/circuit/6394445589905408

Diagram: View attachment 224950
When do you want the timing cycle to start? When the circuit is powered on?
 

Thread Starter

Genosphere

Joined Dec 8, 2020
7
When do you want the timing cycle to start? When the circuit is powered on?
Right when it is powered on, stays active for 3 to 4 seconds to allow audio file to play, then shuts off. In hind sight, building simple audio amp would have been easier, but since when do you get anywhere by doing easy. haha

Thank ericgibbs; ill take a look here in am momnet.

Thanks for the fast replies from both of you.

Here is some of the data i calculated with a DC analysis for the circuit with just the NPN, im guessing is all wrong since the og circuit is messed up. Which may explain why the values in the sim didnt quite match up to calculations. haha
~~~~
Data:
VS=13V; Vcc=5.89V
Ib=6.25mA; Vb=7.05V
Ic=0.0628uA; Vc=6.279V; Vbe=0.8V
Ie=6.25mA; Ve=6.25V
Device during ON state become saturated and acts as a “short,” supply voltage to the capacitor from the “Trigger” pin of 555. SAT: Vb>Ve;Vb>Vc

In the “OFF” state, the transistor enters the “cut-off” region.

~~~
^Probably wrong^
 

eetech00

Joined Jun 8, 2013
2,376
Right when it is powered on, stays active for 3 to 4 seconds to allow audio file to play, then shuts off. In hind sight, building simple audio amp would have been easier, but since when do you get anywhere by doing easy. haha
Then the trigger only requires an RC circuit to trigger the timer at power up like Eric shows in post #10.
 

Thread Starter

Genosphere

Joined Dec 8, 2020
7
Gotch, makes sense to me. Just sucks the NPN or PNP didn't go as planed. I guess thats what learning is all about. Thanks so much everyone.

Might be the last question for this since you all responded really quickly and precisely:
Aside from creating a separate amp circuit, to say boost the audio output of the speaker im using, there really isn't a practical way to use an NPN or PNP transistor in this without doing it just for the hell of it, or would there?

~~~~~~~

After thinking about it, I do recall the method you used eric, finals week must really have me burning out with deadlines at work piled on too. I feel like the board I burned up last night.

Ill have at least something for this evening to show I understand where things went wrong and what I learned.

Thanks again all.
 

Thread Starter

Genosphere

Joined Dec 8, 2020
7
Depends upon exactly what you want the transistors to do.
Well, the idea was to drive it into saturation and use it as a switch to turn on/start the timer once the ignition key is turned, but with the simply use of the diode || R1 referenced above by eric it appears to me that its useless unless i used the transistor(npn) in place of the photocoupler. The photocoupler is more or less a transistor any way so there really isnt much change based on the desired operation which is treating the part as a switch. Now, if i were to pare the npn and pnp together for an amp to boost sound, I believe that would be a much better application for them. The npn would turn on during + signals and the pnp could turn on during - signals; if my memory is correct.
 
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