footswitch controlled SSR project

[d_rom]

Hey all
About a month ago I posted about a terrible pop when using a toggle switch to switch AC from the fast to the slow AC induction motors in my leslie.  The best solution was posted by R.G. (who else?), who said that I should utilize zero-crossing Solid state relays to switch between motors.

I finally found a schematic that addresses this problem, but there are some things that I do not understand about it.

It is found here: http://www.mindthegap.tmfweb.nl/hamles.html

My questions , followed by a drawing of the schematic and the inventor's explanation, are :
1. Where does the footswitch get wired in to this circuit?
2. THe explanation says that when the tip of the TRS is connected to ground, power goes to the fast motor -- this seems to imply that if using a "sustain-type" pedal as recommended, you would have to keep your foot on the pedal to keep the thing going fast -- could I wire a pushbutton switch here instead?
3. What are the other switches (ie S1, S2, S3)
4. What does the symbol in between s2 and 23 that looks like an inverted "T"?
5. Will any type of Diodes and LEDs work here?
6. Are the LEDs and Triacs within the dashed lines an integral part of the SSRs?

I know this is long winded, but any help would be appreciated.  I'm getting rather desperate....



And the explanation:
"The circuit uses a stereo jack as an input for the switch, which can be any switch you choose to use, including industry standard sustain pedal switches with a jack cord and the like, or a Leslie half moon switch, or a modified main-echo-ensemble switch, since the switch is completely electrically isolated from the motor switching circuit.
When the tip of the jack is connected to ground, the motors will switch to fast, when the connection is open the motors will run slow. When the ring of the jack is not connected to ground the motors will stop running, when the ring is connected to ground they will start. This also means that the motors will automatically stop when the jack plug is pulled, and that the motors will always run when a mono jack plug is plugged in (this way you can use a standard foot switch to switch from fast to slow). A couple of LED's indicate the current state of the switch.
The schematic uses a small transformer to supply the power for the relays, but power may also be taken from the filament supply of the Leslie amp, if present. Motor switching takes place on the zero crossing of the motor supply AC, so no pops or crackles or other noises will be induced in the Leslie. The circuit does not contain any moving or otherwise wearing parts so it improves the reliability of the Leslie, which is specially important for road use. But of course you may as well use it at home. Or use it to switch multiple Leslies."

[acromarty]

1. Where does the footswitch get wired in to this circuit?

It looks like the footswitch should be wired in place of switch S3. This switch turns one SSR on and the other off when it is opened or closed. Transistor T1 is wired as an inverting switch, so that when S3 is closed, SSR1 is on and SSR2 is off. When S3 is open, SSR1 should be off and SSR2 is on. You may have to check that SSR1 turns off correctly when S3 is open, as there will be some current flow through D3, SSR1 into the base of T1. If there is any problem with this, make S3 an SPDT switch and remove T1. The switch then connects 0V to either SSR1 or SSR2, turning on the selected motor.

2. THe explanation says that when the tip of the TRS is connected to ground, power goes to the fast motor -- this seems to imply that if using a "sustain-type" pedal as recommended, you would have to keep your foot on the pedal to keep the thing going fast -- could I wire a pushbutton switch here instead?

Yes. Connect a normal latching SPST footswitch as S3.

3. What are the other switches (ie S1, S2, S3)

S1 is the input mains supply fuse.
S2 is the motor power on/off power switch. I would have put this in the +ve supply line rather than the 0V, but it will work as drawn. When this switch is open, both motors are off. When this is closed, the motor selected by S3 is on.
S3 selects either fast or slow motor.

4. What does the symbol in between s2 and 23 that looks like an inverted "T"?

This symbol is a chassis ground point.

5. Will any type of Diodes and LEDs work here?

Yes. D2, D3 and D4 are just indicators. D2 is the on/off indicator, D3 and D4 show which motor is selected.

6. Are the LEDs and Triacs within the dashed lines an integral part of the SSRs?

Yes. A solid state relay consists of an input, usually an LED, optically coupled to an output, in this case a triac type device to allow switching of a.c. loads. Other types are available for d.c. loads. The RC networks around the triac outputs are snubber networks to minimise any voltage spikes when the motor (an inductive load) is turned off.

[d_rom]

Thanks, andy.
But if S1 is the fuse, what the heck is that rectangular symbol that says "500mA"?

I can't thank you enough.
Many a sound man has feared for his system's life whe I engaged my toggle switch, sending a spike through the house mains.

-Dan

[acromarty]

Whoops! I think you're right, the rectangular thing marked 500mA is supposed to be the fuse, and S1 is a mains power switch, rated 250V 1A.
The symbol used on the diagram looks more like a fuse symbol.

On the subject of fuses, I have found the little solid state fuses very useful. I think they are made by Raychem, and are called Polyswitch. They have a low resistance when cold and latch into high resistance if too much current is drawn. The advantage over normal fuses is that they recover again when power is removed and they cool down, so they don't need replacing when they trip. Of course if the excess current is caused by some other fault then the unit won't work until it is fixed, but at least the fuse is just protecting the system and not causing more problems. I replaced the fuse in my Boss brick power supply when I found that running two pedals from the same power supply was blowing the internal fuses, and I haven't had a problem with it since.

[gurutzeta]

d_rom, could we see some pictures of your Frankenleslie?

Thanks