steviejr92
Authorized Vendor
Yeah just noticed that pretty dang smart. Kudos!
A simple Relay Bypass
- Thread starter Chuck D. Bones
- Start date
As in, "judiciously out of sight?"
Brett
Well-known member
Thank you, but I cannot take credit for the idea. I saw it on a switch-mounted relay bypass from Effects Layouts.
Chuck D. Bones
Circuit Wizard
Looks like there is enough clearance around the switch hole on the +9V only board that the insulated washer is not needed.
Did you consider using SMDs for the 555 and 78L09? Would free up some space. An adjustable LDO reg would be a nice alternative to the 78L09.
Did you consider using SMDs for the 555 and 78L09? Would free up some space. An adjustable LDO reg would be a nice alternative to the 78L09.
Brett
Well-known member
I'd be happy to give those changes a shot.
Did you have a particular LDO in mind? I try to find parts that are readily available at Tayda but it looks like they don't have any SMD options for an adjustable LDO regulator.
Chuck D. Bones
Circuit Wizard
There's always Mouser. I'll look into it.
Chuck D. Bones
Circuit Wizard
LM317 is not LDO (low drop-out). We need the LDO feature when we power the pedal with 9V. We could easily lose 2V in an LM317.
steviejr92
Authorized Vendor
Hey man you saw a great idea and implemented it. It’s all about execution in my book.
Oh, I thought the regulator was only for using voltages over 9v. But I guess the idea is to always have the regulator in the circuit for all voltages, with the ability to adjust for as little voltage drop as possible when using 9v, right? If that’s the case, what about keeping the 78L09 but add a little DIP switch to bypass the regulator when running at 9v?
Edit: SMD only, but the Linear LM3045 has a 260mV dropout voltage. It’s brother LM3042 has 350mV dropout voltage (also SMD only). Not cheap either - but deliciously overkill specs!
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Smrtokvitek
Well-known member
I made a relay bypass a few years ago with the smallest PIC (10F322) in the product line with SMDs. There is plenty of room if you want to go that way. I really like @Brett s switch mounting. That's the only thing I don't like about my design. I usually use solid wire to secure it to PCB and hot glue.
szukalski
Well-known member
@Brett @Smrtokvitek - both of your designs are awesome. I think the footswitch-through-board approach is the more practical one (a la Effects Layout), but with added SMD to get the size down. You have to sacrifice a lot of space for the footswitch to avoid shorts, but I think there's enough space to play around with in the SMD world.. a 125B should have enough space for a dual footswitch with relay without causing pain to the PCB..
Brett
Well-known member
Thank you, @szukalski! SMD is certainly an option, and one that I don't mind working with. I DO try to design in through hole because if anyone else ends up with one of my boards, through-hole is usually preferred. In deed, the FS takes up a lot of space but it's possible to design around it. I've designed a board for another @Chuck D. Bones circuit in 125b that uses two of these relay switching systems, all through-hole.
Chuck D. Bones
Circuit Wizard
Move your foot faster! 
But seriously folks, mine has no perceptible lag. The relay should switch in 10ms or less.
But seriously folks, mine has no perceptible lag. The relay should switch in 10ms or less.
Feral Feline
Well-known member
I want nothing more than 9.372 ms
What if you were to change the layout to accommodate the fang style switch? No more glueing...
What if you were to change the layout to accommodate the fang style switch? No more glueing...
szukalski
Well-known member
In general, I think securing any external hardware (switch or jack) to a pcb is just asking for trouble. There’s a risk of mechanical stress if the component fixing comes loose and then the stress is all being taken by the pcb or solder joint.
Chuck D. Bones
Circuit Wizard
The 555 debounces the switch by reacting instantaneously the first time the switch contacts close, then it takes a few 10s of milliseconds for the circuit to recover and be ready to toggle again once the contacts break. That way, contact bounce in the switch does not keep retriggering the 555.
benny_profane
Well-known member
I wouldn’t think so. There is a difference in priority of the threshold and trigger pins between the two, but they are tied together here.
Chuck D. Bones
Circuit Wizard
According to the Texas Instruments & Fairchild datasheets, LM555 & NE555 are identical.
The priority of TRIGGER vs. THRESHOLD is not discussed in the datasheets. That means that priority is an undocumented feature which might be different between two 555 devices depending on who made the part & when. As Grant says above, it's moot for this design because TRIGGER & THRESHOLD are connected together, which precludes a conflict between the two.
The priority of TRIGGER vs. THRESHOLD is not discussed in the datasheets. That means that priority is an undocumented feature which might be different between two 555 devices depending on who made the part & when. As Grant says above, it's moot for this design because TRIGGER & THRESHOLD are connected together, which precludes a conflict between the two.
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