Hello

I am designing a circuit for the first time, so I would like someone with more experience to take a look. It works fine on protoboard but im sure there are things to correct or improve before ordering PCB.

So, what did i do here (tried) :
LED lights up depending on the position
Three fix positions on potenciometer: up, middle, down (0.6v,2.5v,4.3v)
Middle position is executed in window comparator
Delay off for every position around 3s
power supply is 5v from usb
Since the positions are fixed and far from each other I think I don't need hysteresis in circuit?
In an ideal world would be nice to have and delay on (1-2s), but only with minimum components (i dont want to add 555 timer or someting like that).

Thanks in advance for any advice

 

Try adding a 47uf capacitor directly across the base - emitter junction of Q1 for a delayed turn on.

 

That switch will oscillate very well, giving a gradual turn on/turn off over a range close to the changing points. Been there and done that, it really does oscillate very well.

 

Ltspice sim of the delay circuit below:
That about what your protoboard circuit showed?

 

But is there any useful output from the circuit?? OR is this just an LED circuit??

 

Thanks for your responses.

Today i played with the idea that I might get a small delay ON (more precisely in my case Fade) if I limit current that charge capacitor and it works but have drawback. Replaced R9,R12 and added R18 with much larger 220K to limit current to capacitor that means that i affected and Ib so now i have only 4mA trough led (but its ok, these new LEDs are bright even on few mA). One more thing is that when voltage on capacitor fall down to 0.6v transistor closes and i did not found way to fully discarge capacitor (so i losing little on delay).

Outputs from circuit are only LED lights, (potenciometer that is here input is output for another circuit), three positions are
are mechanically defined and switched instantly between positions. No buzzer, i guess ananittarhib wanted to clarify how he understood circuit.

Ltspice sim was realy close what i had here on board, will have to try it myself.

 

Just because a transistor tends to switch off at about 0.7 volts Vbe does not mean that there is no base current when Vbe is less than 0.7 volts. There is still some base current.