Footswitch problem

[rutledj]

I'm trying to wire up an existing Carvin footswitch I have. I'm using Funks PT feeding a 5v regulator. The pos is connected to the 3 relays and I'm switching the grounds.

The footswitch runs the signal through the switch then the diode (in series) back to the ground. Apparently there isn't enough juice to light the LED this way and switch the relay. The LED lights but the relay doesn't change.

Is there another solution to this?

Thanks,
Rut

[heisthl]

put a 100 ohm resistor between the LED leads (parallel)

[glasman]

What is your supply voltage with the footswitch closed? Measure both sides of the regulator. Also what type of rectifier. Doubler, half wave ??

[rutledj]

Tried the 100 ohm and it didn't help.

The regulator is a bridge rectifier into a 7805 regulator. The voltage across the relay falls to about 2.75v when I push the switch.

[glasman]

That explains why the relay is not working.

As I don't know your exact circuit (in this case the transformer winding) I will make a couple of assumptions.

1. You are using the 6.3 (or maybe 5 volt tap) on the tranny.

2. With a full wave bridge and the 6.3v you will only have around 7 volts to the regulator. This is pretty low and I serioously doubt that the regulator will maintain 5 volt output.

Here is what I would do.

1. Rewire the supply as a voltage doubler. This will give you a minimum of around 13 volts if using the 5 volt tap.

2. Add 2 1N4001 diodes in series with the ground leg of the regulator. This will compensate for the voltage drop across your LEDs. These diodes must be forward biased. Means cathode/banded ends towards ground.

This will provide about 6.6 volts output on the regulator and you should have stable regulation. The only other factor I don't know is the coil resistance of your relays, and this does come into play.

[rutledj]

Will this solution cause a problem when the relays are switched using the normal toggle switch on the amp panel (ie, too much voltage?) and do you think it will still be enough voltage if I have 3 footswitches (and 3 LED's) on at the same time?

Thanks,
Rut

[glasman]

Will this solution cause a problem when the relays are switched using the normal toggle switch on the amp panel (ie, too much voltage?) and do you think it will still be enough voltage if I have 3 footswitches (and 3 LED's) on at the same time?

Thanks,
Rut

I really dont think the extra 1.2v is going to be harmful to the relays. The OMRON spec is 120%. If you are concerned, just put a diode in series to drop .6 volts or so.

Gary

[rutledj]

OK. I connected this to the 6.3 v supply (high amperage). When I press the button the LED lights but the relay still doesn't change. The voltage across the regulator stays at 4.95v

My guess is that since the relay is getting it's ground through the switch in series with the LED that it isn't getting close enough to ground to switch.

I tried putting a low value resistor in parallel with the LED (100 - 150 ohm) but it didn't work and kept the led from lighting. Any value larger didn't do anything.

Rut

[glasman]

OK. I connected this to the 6.3 v supply (high amperage). When I press the button the LED lights but the relay still doesn't change. The voltage across the regulator stays at 4.95v

My guess is that since the relay is getting it's ground through the switch in series with the LED that it isn't getting close enough to ground to switch.

I tried putting a low value resistor in parallel with the LED (100 - 150 ohm) but it didn't work and kept the led from lighting. Any value larger didn't do anything.

Rut

Did you put the two (might need three) diodes in the ground leg of the regulator. This will raise the voltage.

[glasman]

Also what is the coil resistance of the coil in the relay?

[tele_player]

Since you've got a 5V regulator, I'm assuming you've got 5V relays. Correct?

Try bypassing the LED completely, see if the relay switches.

Basically, a 6.3v tap is too low to run 5v relays with LEDs and a regulator - unless you use a voltage doubler.

glasman - there's no point using a regulator if you're not going to meet the dropout voltage requirement. A 7805 has a 2V dropout voltage, meaning you must always supply 7V on the input, minimum. If you add, for instance, 2 diodes on the ground lead of the 7805, your minimum input voltage for regulation is 5 + 2 + 1.4 = 8.4V. A 6.3v tap, bridge rectified and filtered, will deliver about 7.5Vdc. Not enough.

[glasman]

Since you've got a 5V regulator, I'm assuming you've got 5V relays. Correct?

Try bypassing the LED completely, see if the relay switches.

Basically, a 6.3v tap is too low to run 5v relays with LEDs and a regulator - unless you use a voltage doubler.

glasman - there's no point using a regulator if you're not going to meet the dropout voltage requirement. A 7805 has a 2V dropout voltage, meaning you must always supply 7V on the input, minimum. If you add, for instance, 2 diodes on the ground lead of the 7805, your minimum input voltage for regulation is 5 + 2 + 1.4 = 8.4V. A 6.3v tap, bridge rectified and filtered, will deliver about 7.5Vdc. Not enough.

Go back and read my previous comments.

[tele_player]

I read them all - just making sure the recommendation for using a doubler is clear.

[heisthl]

I don't know what you're doing wrong but I've sucessfully powered 3 relays without a doubler or a regulator off of the 5V taps with series'd LEDs. The relays I used were mouser 5V 655-V23105A5401A201 and the parallel resistor was 120 ohms across each LED. The PS schematic I used is:

[rutledj]

[qoute]
Did you put the two (might need three) diodes in the ground leg of the regulator. This will raise the voltage.[/quote]

No. I missed this part. I'll try it again later.

Thanks.[/quote]