Need help, with 2 circuits

[iflymyhelishigh]

Hi guys, I am currently trying to build 2 circuits, I am a total electronic noobie.

I want to have 1 circuit beep once for 1 second when I power on my powersupply, then never beep until the supply is turned on again.

I also want to have a circuit that beeps if power is lost to the circuit, I think I have one, and I'm working on building it right now, so that one is covered.

That 1st one, I couldn't find anything on it...

 

[Leftyretro]

Hi guys, I am currently trying to build 2 circuits, I am a total electronic noobie.

I want to have 1 circuit beep once for 1 second when I power on my powersupply, then never beep until the supply is turned on again.

I also want to have a circuit that beeps if power is lost to the circuit, I think I have one, and I'm working on building it right now, so that one is covered.

That 1st one, I couldn't find anything on it...

Search for 555 timer circuits, should be a simple solution.

Lefty

 

[iflymyhelishigh]

Lefty, I searched a whole lot and couldn't find anything.

 

[Henry T]

Hmm, thinking of a RC-combination and a transistor. RC-time would be one second, and when it's fully charged it switches of the transistor?

 

[transistor495]

For charging the Cap, one end should go to the supply line and other to the transistor base?! Then the parallel R will make the transistor always ON I think. Anyway the Cap should be discharged every time when the unit switched off.

 

[ericgibbs]

Lefty, I searched a whole lot and couldn't find anything.

hi,
Look at these examples:


**broken link removed**

 

[ezpcb.com]

combine 2 circuits will do: a controlable oscillator circuit plus a pulse width gererator. the power on pulse width could be get with a RC circuit and a schimdt trigger.

 

[flat5]

"I want to have 1 circuit beep once for 1 second when I power on my power supply, then never beep until the supply is turned on again."

Maybe this will do. Comments please.

Edit: Oops! Add a 1M resistor across the cap.

 

[ericgibbs]

"I want to have 1 circuit beep once for 1 second when I power on my power supply, then never beep until the supply is turned on again."

Maybe this will do. Comments please.

Edit: Oops! Add a 1M resistor across the cap.

hi,
Whats the 1M0 resistor across the cap do.???

 

[Henry T]

See, that's what I mean, and then indeed you should add a extra resistor across the cap so it discharges when the power is turned off...

 

[ericgibbs]

See, that's what I mean, and then indeed you should add a extra resistor across the cap so it discharges when the power is turned off...

But dosnt the cap discharge back thru the 100K pot when the +5v dies away.???

 

[Ubergeek63]

See, that's what I mean, and then indeed you should add a extra resistor across the cap so it discharges when the power is turned off...

or a simple diode across VR1 to discharge it as the supply rail collapses.

 

[ericgibbs]

"I want to have 1 circuit beep once for 1 second when I power on my power supply, then never beep until the supply is turned on again."

Maybe this will do. Comments please.

Edit: Oops! Add a 1M resistor across the cap.

hi,
Your circuit should give a 'beep' when powered up.

Initially the cap is discharged, when the +5V is applied the cap charges via the 100K towards +5V.
While the cap is charging the base of the transistor is forward biassed, so the transistor is on.
When the voltage on the cap rises to within 0.6V of 5V [+4.4V] the transistor will switch off.

When the +5V supply is switched off, the cap will discharge thru the 100K pot as the +5V slowly decays
[ back thru the rest of the circuits supplied by the +5v]

 

[flat5]

I did not know what the rest of the circuits will be or where the switch will be so I thought it might be a good idea to add a discharge resistor.

To avoid math and the facts that I would get it wrong anyway + the wide cap tolerance and other variables (what will Vcc be?), the pot will set the timing.

 

[ericgibbs]

I did not know what the rest of the circuits will be or where the switch will be so I thought it might be a good idea to add a discharge resistor.

To avoid math and the facts that I would get it wrong anyway + the wide cap tolerance and other variables (what will Vcc be?), the pot will set the timing.

The problem with adding a 1M0, this together with the leakage resistance of the 100uF could hold the transistor ON.

Yes the pot will set the charge time for the cap.
If you mean the Vcc on the transistor collector wrt 0V, when the transistor is conducting it could be about 4.8V.

 

[Externet]

A capacitor in series with a DC beeper B1 connected to the 'powered-on rail' node will only beep while charging at turn on. The 1-second is to be tailored by the capacitor value.
A second DC beeper B2 in parallel to the capacitor will sound at discharge when turned off or lose power.
Beepers can have different tones if preferred.

Would this work ?

+rail----------||-------J------|>|-----B1-------gnd

+rail----|<|---B2------J

J=junction node
---|>|--- = diode

 

[flat5]

"If you mean the Vcc on the transistor collector wrt 0V, when the transistor is conducting it could be about 4.8V."

wrt?

No, I mean I don't exactly know the base voltages that will turn on (enough) and off the transistor to set the timing without building and testing the circuit. Hence the pot.

 

[flat5]

Externet, that's a good solution.

 

[ericgibbs]

"If you mean the Vcc on the transistor collector wrt 0V, when the transistor is conducting it could be about 4.8V."

wrt?

No, I mean I don't exactly know the base voltages that will turn on (enough) and off the transistor to set the timing without building and testing the circuit. Hence the pot.

hi,
The 'wrt' is shorthand way of writing 'with respect to', all that means in this case, is the -V lead of a volt meter connected to 0V/Common as the reference level. [ with the +V lead to the collector]

The turn on voltage for most silicon transistors is 0.6V~0.65V

So while the cap voltage is less than [+5V - 0.6V] the transistor will be on.

 

[Externet]

Would this work ?

+rail----------||-------J------|>|-----B1-------gnd

+rail----|<|---B2------J

J=junction node
---|>|--- = diode

Am I wrong and should be

+rail----------||-------J------|>|-----B1-------gnd

J-----------|<|----------B2------------gnd