Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Switching circuit and footswitch for new amp
Switching circuit and footswitch for new amp
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th September 2019, 03:29 PM   #11
Audio1Man is offline Audio1Man  United States
diyAudio Member
 
Join Date: Feb 2010
Location: Thousand Oaks, CA.
Just wire a LED in series with the FOOTSWITCH. Watch out for the current that is needed to control the relays as it flows through the LED.
Duke
  Reply With Quote
Old 11th September 2019, 08:44 PM   #12
akkar is offline akkar  Italy
diyAudio Member
 
Join Date: Aug 2010
The current for the relay coil is 40mA so is too much for a led
  Reply With Quote
Old 11th September 2019, 10:48 PM   #13
Audio1Man is offline Audio1Man  United States
diyAudio Member
 
Join Date: Feb 2010
Location: Thousand Oaks, CA.
Shunt the LED with 50-75 ohms. The 2.x volt drop across the the resistor will carry most of the current. The pickup voltage across the relay could be a problem, if so add a capacitor across the LED.
  Reply With Quote
Old 15th September 2019, 11:00 PM   #14
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by Audio1Man View Post
Shunt the LED with 50-75 ohms. The 2.x volt drop across the the resistor will carry most of the current.
I had exactly the same thought earlier. It's the simplest solution, however, it is worth a mention that this idea requires that V+ be at about two volts greater than the voltage needed to actuate the relay. If you're running 12V relays on a 12V power supply, the extra voltage drop of the LED might stop the relay from closing reliably - the relay will only ever "see" 10 volts or so.

Also, I would suggest putting a regular silicon rectifier diode (1N4001 or similar) in reverse parallel with the LED, to protect the LED from reverse-voltage spikes when the relay is turned off.

-Gnobuddy
  Reply With Quote
Old 18th September 2019, 02:55 PM   #15
akkar is offline akkar  Italy
diyAudio Member
 
Join Date: Aug 2010
Quote:
Originally Posted by Gnobuddy View Post
I had exactly the same thought earlier. It's the simplest solution, however, it is worth a mention that this idea requires that V+ be at about two volts greater than the voltage needed to actuate the relay. If you're running 12V relays on a 12V power supply, the extra voltage drop of the LED might stop the relay from closing reliably - the relay will only ever "see" 10 volts or so.

Also, I would suggest putting a regular silicon rectifier diode (1N4001 or similar) in reverse parallel with the LED, to protect the LED from reverse-voltage spikes when the relay is turned off.

-Gnobuddy
The datasheet of the 12V realay I'd like to use here https://omronfs.omron.com/en_US/ecb/...f/en-g5v_2.pdf

on page 2 says it will work with 75% of rated voltage.... so maybe a 12Vcc would be enough?
  Reply With Quote
Old 18th September 2019, 04:27 PM   #16
akkar is offline akkar  Italy
diyAudio Member
 
Join Date: Aug 2010
Click the image to open in full size.
  Reply With Quote
Old 18th September 2019, 08:00 PM   #17
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by akkar View Post
<circuit diagram snipped>
Since your relays will work on 9V, that looks like a good starting point.

I suggest 1N4148s or 1N914s for the four protection diodes. They are easy to find, fast, and will handle the currents involved in this application.

You may find that you need to adjust the value of those 47 ohm resistors by trial and error - if they're too small, the LEDs in the foot-pedal won't light, and if they're too big, the LEDs will be too bright, and might even burn out.

Also, this is one situation where I would avoid high-efficiency LEDs - some of these will light with less than 0.1 mA, and in this particular case, that is not a good thing. Old-fashioned low efficiency LEDs that require 10 - 20 mA is what you want for this particular application.


-Gnobuddy
  Reply With Quote
Old 19th September 2019, 07:59 AM   #18
akkar is offline akkar  Italy
diyAudio Member
 
Join Date: Aug 2010
Quote:
Originally Posted by Gnobuddy View Post
Since your relays will work on 9V, that looks like a good starting point.

I suggest 1N4148s or 1N914s for the four protection diodes. They are easy to find, fast, and will handle the currents involved in this application.

You may find that you need to adjust the value of those 47 ohm resistors by trial and error - if they're too small, the LEDs in the foot-pedal won't light, and if they're too big, the LEDs will be too bright, and might even burn out.

Also, this is one situation where I would avoid high-efficiency LEDs - some of these will light with less than 0.1 mA, and in this particular case, that is not a good thing. Old-fashioned low efficiency LEDs that require 10 - 20 mA is what you want for this particular application.


-Gnobuddy
Thanks for the suggestions!

Why is better to not use low current LEDs in this case?
  Reply With Quote
Old 19th September 2019, 02:55 PM   #19
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by akkar View Post
Why is better to not use low current LEDs in this case?
Putting a resistor in parallel with an LED is a "touchy" circuit - if the current through the circuit is a little bit too small, the LED won't light. If the current through it is a little bit too big, the LED will be too bright, or burn out.

I think the circuit becomes less touchy when the LED current is a larger fraction of the total current in the circuit.

Consider: if you have 20 mA LED current and 40 mA total current, you also have 20 mA in the resistor. If the 40 mA current increases by 10% to 44 mA, most of the change goes into the LED, so the LED current is up to about 24 mA, a 20% increase. That's probably acceptable.

Now suppose you have a high-efficiency LED that only needs 0.1 mA to light up. The resistor has to carry the remaining 39.9 mA. If the total 40 mA current increases to 44 mA as before, the LED current now rises from 0.1 mA to 4.1 mA. That's a 4100% increase!

The LED may cope with the 4.1 mA current, but if it was bright enough at 0.1 mA, then it will be painfully bright at 4.1 mA, maybe even damagingly bright. Nobody wants a guitar pedal with an eye-wateringly bright LED glaring up at them from a dark stage floor!

So my concern is that the circuit will be much more "touchy" with high-efficiency LEDs. The unavoidable small changes in circuit current will cause much bigger changes in LED brightness if you use high-eta LEDs.

(Those small changes in circuit current can be caused by slight changes in V+, or the change in resistance of the relay coils with temperature, or resistor temperature coefficient, or the temperature coefficient of the voltage drops across the LEDs themselves.)


-Gnobuddy
  Reply With Quote
Old 19th September 2019, 11:57 PM   #20
Audio1Man is offline Audio1Man  United States
diyAudio Member
 
Join Date: Feb 2010
Location: Thousand Oaks, CA.
You can always add a resistor in series with the foot switch LED's
Duke
  Reply With Quote

Reply


Switching circuit and footswitch for new ampHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Mesa Mark II footswitch circuit draws from heaters, unbalanced and noisy results TankAudio Instruments and Amps 3 10th February 2017 04:32 AM
Conceptual question about switching tonestacks in circuit. Channel switching amp garybdmd Instruments and Amps 2 3rd May 2016 06:03 PM
Where to put a buffer circuit in this switching VU circuit I came up with? HiFi1972 Construction Tips 0 9th March 2013 04:55 PM
circuit switching ross21 Solid State 4 15th July 2011 07:50 AM
switching circuit rfarn Parts 6 14th June 2008 02:03 PM


New To Site? Need Help?

All times are GMT. The time now is 06:02 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki