Jump to content
Electronics-Lab.com Community

Help me..problem to triggered relay

Guest 89Panadol

Recommended Posts

Guest 89Panadol

Hai everyone...I have problem with my Ultrasonic Radar project..

The problem is: 1)Motion detector cannot triggered relay.
                        2)When output from ultrasonic radar not connected to relay,the output voltage is almost 9v when
                        it detect motion.
                        3)When output from ultrasonic radar connected to relay,the output voltage is just 2 v when it detect
                         motion(not enough to triggered relay)

This circuit use a  pair of transistor BC547 as output to triggered relay.

How i  can increased the voltage when ultrasonic radar connected to relay..

Link to project



Link to comment
Share on other sites

  • 1 month later...

Are you still there and still interested, 89Panadol?

Most likely your relay has a coil with too low a resistance.  What type of relay is it and what is its coil resistance?  How much current does the coil draw if connected directly from your 12 volt supply to ground?  How does that compare with the maximum current rating of your darlington output stage transistors?

What is the current capability of your 12 volt power supply?  Is it capable of driving the relay coil directly?  Measure the 12 volt supply while the device is trying to close the relay to be sure it stays at 12 volts.

Your darlington output stage would have a current gain of at least 10,000, which is plenty for the drive current available from the 4093 gate via the 100K resistor.  The BC547/8 has a collector current rating of only 100ma which is OK for many small relays but not necessarily for a large relay with a low resistance coil.  But I would expect the transistor to fry if you tried to pull too much current.  Are both transistors still OK?  If TR2 burned out TR1 alone would probably lack sufficient gain to drive a low resistance relay coil.

Try a more sensitive relay, perhaps a solid-state-relay, depending upon what your load is.  And check your output transistors.


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...