A Switching Scheme

Original effect designs complete with verified schematics, layouts and instructions. All project were freely contributed by members and cannot be used for commercial purposes without consent of the respective owners of the copyright.
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chris1001
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Post by chris1001 »

Built Mictesters Schmitt inverter circuit up today, works well but doesnt respond to quick on/off cycling of the momentary footswitch, the time taken for the caps to charge/discharge is too long. Whats the easy fix, lower the 1M resistor or reduce the size of the caps?

Cheers


On power up, the 100n cap is discharged (cap voltage=0), so the first inverter output goes high, causing the 220n to charge up to +9V slowly through the 1M resistor. The high level on the first inverter output also causes the second inverter output to go low, which reinforces the low at the input of the first inverter due to the positive feedback provided by the 100k resistor. The LED is on and the "Output" is high.

When you press the switch, the 9V of charge on the 220n cap is dumped onto the 100n cap, causing the voltage at the first inverter's input to go higher than 6V, which is enough to make it's output change state. This turns the LED off and the "Output" terminal goes low.

If you held the switch closed, nothing would happen because the charge on the 220n is only higher than the threshold for a fraction of a second. It quickly is dumped into the 100n and through the 100k resistor. This is also what prevents "switch bounce" to cause false triggering.

deafbutpicky
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Post by deafbutpicky »

Whats the problem though. You mean the time between fast on/off switching?
I build it too and the switching response from on to off and back, one at a time, is as fast as
a normal switch. You woudn't engage the pedal for just one note, right?
I'm using capacitors to replace my guitar effects and give more clarity to the sound.

chris1001
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Post by chris1001 »

Thanks for the solution, I'll implement it straight away! I found that the response was a lot slower than the regular Ibanez or Boss flip-flop, you might not ever activate a pedal for a single note, but you might accidently switch a pedal on when playing live (and in the dark) and need to switch it off a split second later. Its kind of embarrassing in front of a large audience.....

chris1001
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Post by chris1001 »

Update: Mictesters Schmitt inverter circuit works well, with the LED and relay staying in sync when the power is pulled, regardless of whether the pedal was 'on' or in bypass. However, it only works becasue I've omitted the 100n cap, - previously if the power was pulled and the pedal was in bypass, on re-connection of the power the LED would illuminate and the relay would still be in bypass.

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electrosonic
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Post by electrosonic »

On the first page of this thread, mice tester posted this...
The only addition I sometimes make to this circuit is to use a CMOS bistable to feed the anode of the diode - the "+" point. I use a 4013 configured with one side as a bistable (pin 1 or 13 feeds the switching circuit directly), and the other side as a power-on reset and debounce circuit, or I use a 4093 quad schmitt NAND with two gates for the bistable, one for debounce and one for switch-on reset. Either circuit then allows the use of a momentary switch.
Any idea how to wire up a "switch-on reset"

Andrew.

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Groovenut
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Post by Groovenut »

LC relay with jacks comp.jpg
Hey all, I just finished this design for incorporating the switching into some of the pedals I build. I like to keep things modular at this point, but its easy enough to incorporate into a full board design.

This is designed to go with a latching Carling SPST with cutouts for the jacks. It works a charm! I will be using it on the V2 prototype of the LPD MegaDEN I am putting together. I will post completed pics.

For scale this fits nicely inside a 1590B about 2.25"across jack mounting faces

roseblood11
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Post by roseblood11 »

Nice pcb for madbean or musicpcb...

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Post by bluescage »

really nice design!

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Groovenut
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Post by Groovenut »

Thanks guys! :D I also have a design that uses a standard PCB mount DPDT that I will be making once my supply of Carlings is depleted. It's actually a smaller footprint as well. I will be ordering a batch of these soon if anyone is interested just let me know. I am currently working up a momentary switch version too and will post those results as I finish.

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electrosonic
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Post by electrosonic »

I have made a similar switching board, it sits at the top of a 1590BB.
Image

Andrew.

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Groovenut
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Post by Groovenut »

Andrew,

Thats brilliant! No width issues when using different enclosures, a great place for the DC input and LED, and still plenty of room for a battery. :applause:

Great design and very efficient!

Law

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meffcio
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Post by meffcio »

Mictester, will this one do?
electrosonic wrote:I have made a similar switching board, it sits at the top of a 1590BB.
Image
Great one! Certainly something I want to design for myself too.

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electrosonic
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Post by electrosonic »

I am not Mictester but...

There are three types of relays on that data sheet

1. Non latch type - the relay needs a current flowing through it to stay on

2. Single coil latch type - this is stable in either on or off position without any current through it. A current pulse through the coil in one direction turns it on and a current pulse in the other direct turns it off. This is the one used in Mictester's design.

3. Double coil latch type - this is similar to 2. except it has two coils, a current pulse in one coil turns it on and a current pulse in the other coil turns it off

I guess the other consideration is how large the current pulse needs to be to reliably switch the relay. You might need to alter the cap size if you change to a different brand of relays I guess.

Andrew.

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p_wats
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Post by p_wats »

Where are you guys finding good prices on latching SPST switches? Smallbear wants $7 a pop for the Carling ones!

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electrosonic
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Post by electrosonic »

I figure the jacks and the switches take the most abuse, so I use good quality parts there. Carling switches and Neutrik jacks. I can find Carling SPST switches for about $7 locally (no shipping anyways) That is the best price I have found. Tayda has cheaper switches but I am not sure of the quality.

Andrew.

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mictester
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Post by mictester »

meffcio wrote:Mictester, will this one do?
The EA2-5S or 6S will be perfect. These are single coil latching with a coil rating of either 5 or 6 Volts. These will give you the advantage of the ultra-low consumption!
"Why is it humming?" "Because it doesn't know the words!"

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Post by p_wats »

electrosonic wrote:I figure the jacks and the switches take the most abuse, so I use good quality parts there. Carling switches and Neutrik jacks. I can find Carling SPST switches for about $7 locally (no shipping anyways) That is the best price I have found. Tayda has cheaper switches but I am not sure of the quality.

Andrew.
Tayda only seems to have momentary SPST switches (I have some of those and they seem identical to the Carling ones). I'll keep searching!

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Post by mmolteratx »

Here's a drop in PCB that uses a momentary switch. Haven't yet built it, but all looks good. 1.1375" x 1.0500".

Image

.brd - http://dl.dropbox.com/u/8021347/Relay.brd
.sch - http://dl.dropbox.com/u/8021347/Relay.sch

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Post by jubal81 »

Some really impressive work here guys. Mind checking my double relay schematic for goofs?

Image

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mictester
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Post by mictester »

jubal81 wrote:Some really impressive work here guys. Mind checking my double relay schematic for goofs?
Thank you. Your schematic looks OK.

Incidentally, if you're uncomfortable with powering the relay from the output of a gate, you can use a PNP transistor with the emitter to +9V, collector to the two transistor capacitor discharge circuit, and base fed from the bistable through a 5k6 resistor. You don't need to use the last inverter (you want "low" to be active). You'll slightly increase the current drawn (by some µA!), but this may be more robust long-term. You also "win" two inverters, so you could have three relays.....
"Why is it humming?" "Because it doesn't know the words!"

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