Putting components on toggle switches

canman · April 08, 2015, 07:22:11 PM

I really need to get better at working with switches and I figured this would be a good place to start. I want to put the MOSFET clippers of this circuit on a switch, and switch between the MOSFETs and some kind of diodes.

So, looking at this layout...the clippers are easy to spot, but my problem is putting them on a switch! This is my logic thus far, so if you guys could let me know if my logic is correct I'd be really grateful!

I *think* I need to link the source to gate on both MOSFETs, and hook up a wire to where the source would connect on the board in both spots. Or would I connect a wire to the left MOSFET source, and a wire to the right MOSFT drain?? (I hope that makes sense!) Then I'd take those two wires and hook them up to the middle lugs of a DPDT on/off/on. Then on a set of lugs on the end of the switch, I'd connect the clippers...gate and drain on one lug, source on the other lug (and naturally, flipped around for the other MOSFET). Then on the other set of lugs, maybe LED clipping or something.

Is this logic correct? I'm pretty sure I have the switch lugs correct...it's the wires from the board to the switch that are getting me confused.

ubersam · April 08, 2015, 08:17:10 PM

Look at the schematic of the circuit to see how the mosfets are connected. I think you'd get a better idea of how to do the switching if you look at the schematic.

mth5044 · April 08, 2015, 08:17:46 PM

It's much easier to see if you have the schematic. For wiring, you can connect the wires anywhere on the strip. You can even connect them to the far right at the end of the board if you don't want wires coming from the middle.

Drawing a picture is the easiest way to envision it, but your description of how to solder onto the swtich sounds like it is correct.

canman · April 08, 2015, 09:25:56 PM

I knew I was forgetting something!! I totally spaced posting a schematic...dang it. Here's a scheme:

So it looks like I'd connect a wire from the drain/gate of the MOSFET on the right side of the vero (first MOSFET on the schematic though) and then a wire connecting to the source of the MOSFET on the left side (second MOSFET in the schematic). Looks like the diode is left out on the vero, no biggie.

If that's correct, do I need to jumper so that DGS are all connected on the vero (even though the transistors aren't actually on the vero)?

I feel like simple diode clippers would be a bit simpler to mess around with switching...that may have been a better place to start

$:-\$

snarblinge · April 08, 2015, 10:08:42 PM

does this help?

http://www.beavisaudio.com/techpages/switches/

Tony Forestiere · April 08, 2015, 10:24:25 PM

See the two leads of each MOSFET tied together? Think of it as a clipping diode. A DPDT does nice switching between two (dual) lead components.

canman · April 09, 2015, 12:00:43 AM

The Beavis link does help some, but what's throwing me off is the link on the veroboard...I'm not sure where the wires actually need to come from to go to the switch. It would be easy enough to put just one FET on a switch but having two is driving me crazy for some reason.

Adding a switch to the veroboard above means that the locations of the MOSFETs all need to be linked, right? If I can just figure that out then everything else should make sense. These two stupid wires that would go to the switch are just stumping me!!

ubersam · April 09, 2015, 02:17:00 AM

Your vero layout does not have the 1N34 so just ignore that on the schematic, pretend it's a wire. See how the Drain & Gate of each mosfet is tied together? Consider that the Anode. The Source of each mosfet will be the Cathode. There is your anti-parallel "diode" pair.

If I were going to make that switchable with another diode pair using a spdt toggle, this is how I'd do it: https://www.dropbox.com/s/n7k5sy5alf0bkdt/TOGGLE.jpg?dl=0 (easier to just draw it).

mth5044 · April 09, 2015, 08:55:48 AM

There are two end holes of strips left on the bottom right of the board. Your two wires will go in the last two holes (all the other holes are filled with wires). Trace the top strip you just wired back to the left, you see it's connected to S of the left transistor and he D and G of the right via the jumper. Now trace the lower strip you just wired. See that it is connected to the D and G of the left transistor via jumper and the S of the right transistor.

Now when you want to add your switch, those transistors will obviously not be there, but the wires will be running to the strips that connect to their positions. When you hook up the switch and have it on MOSFET mode, it will he just like those transistors are in that same position, but floating up on the switch.

If the whole three pin versus two pin is throwing you, you're just shorting two of the pins together, so you can treat them as one pin when it comes to switching.

Mark Hammer · April 09, 2015, 09:25:51 AM

I regularly mount components on toggles, and will note that this CAN pose a small risk. If you're like me, and do mostly one-offs, you may find yourself twisting wires or struggling to get the toggle to reach or fit in the hole you've provided for it. That "struggle" can occasionally result in component leads fracturing away from the solder lugs on the toggles. It is easily fixed, but is one more thing to keep an eye out for when troubleshooting those FX that "worked before I boxed it up".

canman · April 09, 2015, 10:53:45 AM

Thanks for all the replies, I really appreciate it! I'll be sure to work carefully Mark...I've had my share of broken components on switches before, drives me nuts!

Quote from: mth5044 on April 09, 2015, 08:55:48 AM
There are two end holes of strips left on the bottom right of the board. Your two wires will go in the last two holes (all the other holes are filled with wires). Trace the top strip you just wired back to the left, you see it's connected to S of the left transistor and he D and G of the right via the jumper. Now trace the lower strip you just wired. See that it is connected to the D and G of the left transistor via jumper and the S of the right transistor.

Now when you want to add your switch, those transistors will obviously not be there, but the wires will be running to the strips that connect to their positions. When you hook up the switch and have it on MOSFET mode, it will he just like those transistors are in that same position, but floating up on the switch.

If the whole three pin versus two pin is throwing you, you're just shorting two of the pins together, so you can treat them as one pin when it comes to switching.

This is awesome, thanks for spelling this out for me! I'm starting to understand a bit more here, maybe I'll stare at the vero and schematic in conjunction with your explanation and see if I can completely understand everything. If I'm reading things correctly, the transistor on the right's D/G is connected to S via the 1n cap...does this make it so I don't need to jumper the source to the drain and gate?

Sorry for all of these questions...like I said, for whatever reason, I just can't get my mind around transistors on a switch.

duck_arse · April 09, 2015, 11:33:06 AM

get a little bit of vero, big enuff for the 2 mosfets, the switch connections, and yer alt clippers. wire the mosfets (going from the vero shown above) so each mosfets gate shorts to its own drain. then the source of one shorts to the G-D of the other, twice. now pick a mosfet, take its G-D as one connection out, and its S connection as the other.

mount the switch on the board via short wires, fly fewer wires back to the board, every thing is terminated as well as it can be then.

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Putting components on toggle switches