Problem with 555 Door Bell Circuit

[mtn_silviu]

Hello!
I tried to make this simple Door Bell Circuit,the ding-dong type. Unfortunately it didn't went too well,something is wrong and i don't know why.

http://cdselectronics.com/kits/two tone door bell.htm

I made the PCB in Sprint Layout,made it twice and it just doesnt do notting when i push the button. Checked the components,solder problems..i have no idea.

Can someone tell me if the circuit is wrong? I used NE555P,2N7000TA and a new 1W speaker.

Many thanks!

 

[esp1]

hi,
Is your posted image of the PCB showing the copper track side of the PCB or the Component side?.

E

 

[chuckey]

have you not got a DVM to fault find the circuit? Are you sure you have put the FET in the right way around?
Frank

 

[mtn_silviu]

Hello,and thanks for the reply.
@esp1 The image is showing the component side.
@chuckey Yes,i have a Digital Volt Meter, what should i probe with it? Also,i'm pretty sure i put the MOSFET in the right way around.

 

[mtn_silviu]

Can someone tell me if the circuit is fine and should work? I really don't know what is wrong,usually i make good PCB without soldering problems and stuff. Started using another design,but takes time to gather everything.

 

[Warpspeed]

Can someone tell me if the circuit is fine and should work?

I have just traced it all out and there are several problems with this circuit and it cannot possibly ever work as shown. Its not just one mistake, there are several.

Your best bet will be to start again with a different circuit.

 

[Audioguru]

I see diode #2 in the wrong location:

 

[Warpspeed]

Ah yes !
That certainly changes things.

 

[mtn_silviu]

Well..the original circuit and the corrected one are almost the same,exept for the P-CHANNEL MOSFET in the corrected one. Is that the main problem?

 

[esp1]

hi agu,
Unless I am having a senior moment, the circuits you have posted 'corrected and original' are the same.?
The diode which is crossed out is not in that position on the original circuit.

The original circuit runs OK in LTSpice.

Eric

 

[sathiyanarayananL]

hi,

the cap in series with speaker is 100uf which a too large capacitance. placing capacitors in series in audio circuits is to eliminate any undesired dc signal. replace it by 33pf or 1nf ceramic cap or just remove it and check.

 

[c_mitra]

replace it by 33pf or 1nf ceramic cap or just remove it and check.

Not a good suggestion; at audio frequencies 33pf or 1nf capacitor will never transfer any power to drive a small speaker. What will be the impedance of 33pF at 1kHz?

 

[mtn_silviu]

Hi esp1,
I can clearly see the Ding-Dong waveform there,thanks for your time. Looks like this circuit is working and something is wrong with my PCB,components or soldering, I should start checking what I missed. It will take some time,since I'm completely out of 555's and the ones I have I suspect they are damaged.

 

[esp1]

hi mtn,
What is the impedance of the speaker you are using.?
Also are you using a 9V, PP3 type battery or bench power supply.?

E

EDIT:
Checked you PCB, it looks OK to me.

 

[mtn_silviu]

hi esp1.
Well, my PCB is a little ugly,it's not one of my best ones. I'm using a QW 8Ohm speaker and a bench power supply. Now i have to wait for some new components,this time i'm sure i won't do a mess. Thanks again for your time.

 

[c_mitra]

Can you estimate the power consumption and calculate or estimate how long it will work on a 9V transistor battery? What can be done to reduce the power consumption? Suggest some simple changes that can reduce the power consumption.

 

[crutschow]

.........................
What can be done to reduce the power consumption? Suggest some simple changes that can reduce the power consumption.

You can reduce the quiescent power to zero by using the PB to power the whole circuit.

 

[Audioguru]

I corrected the hand-sketched schematic by moving diode #2 to the correct location and adding the switch.

The speaker is supposed to produce a higher frequency buzz when the switch is pushed then produce a lower frequency buzz when the switch is released as timed by the capacitors.
If the switch powers the 555 then there is no current drawn when the switch is released so the second lower frequency buzz will not ne produced.

The Mosfet turns off the 555 after the second lower frequency buzz then the battery should last for years if the switch is not pushed often.

 

[mtn_silviu]

Hello again.
I managed to finish the PCB and it works perfectly. Looks like my first 555 IC was damaged,i had it replaced but there was something else.. in the first image i have uploaded,you can see a very tiny copper track,size of a hair,running all the way around the PCB. That track acted like i was pressing the doorbell button. It took me some hours to figure it out since i really wasn't expecting something like that. It's not the most pleasant smooth sound,but it does the job.

I also used a BD140 for amplification, a larger speaker and had the 100uF capacitor removed. Used a 500mA wall adapter with a 15000uF capacitor.

 

[KlausST]

Hi,

Your circuit gives DC to the speaker. Usually they don't like this.

Klaus