Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Dummy circuit always works !?

Status
Not open for further replies.

joseche

New Member
Hi all,

My first soldering project is a gift for my GF.

The schematic is at the left :
Velleman Sweetheart

The funny thing is that all the leds are on, but none blinking !?

What should I look for on the board ?, how can all the leds be on but none blinking !?, are the transistors damaged ?

Thanks
 
Last edited:
Hi,

there is not much to do wrong.

Check the polarity of C1 and C2.

The BC547 should be connected as shown in the attachment. (top view)

Boncuk
 

Attachments

  • BC547-1.gif
    BC547-1.gif
    7.1 KB · Views: 184
  • BC547-SYM.gif
    BC547-SYM.gif
    3.9 KB · Views: 188
Last edited:
Hi,

there is not much to do wrong.

Check the polarity of C1 and C2.

The BC547 should be connected as shown in the attachment. (top view)

Boncuk

I think I did it right with the transistors but however,

Can I use the multimeter to measure the resistance between Emiter and Colector in the transistors, it should give me 1 since the transistor should be Off, right ?
 
I made that exact same kit at lunchtime at work about 10 years ago. I've never scored more points with more women in my life. Best of all is the battery back up. It always keeps beating.
 
I think I did it right with the transistors but however,

Can I use the multimeter to measure the resistance between Emiter and Colector in the transistors, it should give me 1 since the transistor should be Off, right ?

You didn't mention the polarity of the electrolytic caps C1 and C2?

Measuring a transistor while power is being applied and seeing the transistor switched "on" (because of the LEDs) is unnecessary.

Recheck your circuit.

Boncuk
 
id short capacitor negative pin to ground for a quick transistor test, I'd also say to check soldering on capacitors....
 
I just did a rough calculation.

Assuming they are red LEDs then they have a pd of about 1.8 Volt.

1.8 * 4 = 7.2 Volt. (9 - 7.2)/1.2 = 1.5 mA.

This not enough current to light the LEDs.

So it would be better if you run it from 12 Volt.

Let me know if it does not work at 12 Volt.
 
I just did a rough calculation.

Assuming they are red LEDs then they have a pd of about 1.8 Volt.

1.8 * 4 = 7.2 Volt. (9 - 7.2)/1.2 = 1.5 mA.


This not enough current to light the LEDs.

So it would be better if you run it from 12 Volt.

Let me know if it does not work at 12 Volt.

The OP mentioned the LEDs are steadily on - not off.
 
The OP mentioned the LEDs are steadily on - not off.

Thanks, I missed that.

Those LEDs must glow on very little current. They normally need more than that.

What voltage do you measure on the collectors wrt Gnd?

What happens if you short the base of one transistor to Gnd?
 
Last edited:
Those LEDs must glow on very little current. They normally need more than that.
Yes, I guess if the leds were blinking it will glow more
What voltage do you measure on the collectors wrt Gnd?
That is to turn it on and measure the voltage with the possitive connected to the collector and ground on the battery ?
What happens if you short the base of one transistor to Gnd?
Will try it !

Thanks for replying
 
Yes, I guess if the leds were blinking it will glow more

That is to turn it on and measure the voltage with the possitive connected to the collector and ground on the battery ? Yes

Will try it !

Thanks for replying

You're welcome.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top