3 way soft latching switch circuit - Page 1
Forum section: electronics / projects

author: Tim K
author_rank: Newbie
timestamp: May 16, 2014, 04:52:02 am
content: David, I just saw your video on the worlds simplest soft latching power switch circuit and was very impressed both by the circuit design and your explanation.I'm a self-taught tinkerer and for the last few years I've been designing and building guitar effects pedals. Now I'm moving on to bigger and better (read heavier and more expensive) things. I'm nearly finished with the design for a three channel guitar amplifier. The switching circuit uses a discrete transistor network for switching various components in and out of the audio circuit and requires power at one of three points depending on what channel needs to be active.I'm looking for a way to use momentary switches to switch power to only one of the three channels at a time. This means that if channel one is active (i.e. constant voltage is being supplied to the transistor network for channel one) and I press the button to activate channel three, channel one will no longer be active and channel three will have a constant voltage. The switching must happen very quickly and any channel must be able to be activated in any order. I also need either a default channel or the last selected channel to be active when the amplifier is first turned on. Any ideas?I know I can achieve this with some chip programming, but that means learning a whole new technology and acquiring more equipment, so I would rather keep this discrete.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: May 16, 2014, 02:53:19 pm
content: Hi,10 years ago I designed simple circuit - something that might help You.It's one of four latching switch.The only problem is with storing which channel was used before turning off.Here, the circuit's power on default condition (number of active channel) is detremined by C3 capacitor connection.The circuit is not ideal but it is simple.Oh,If You press two switches at one time (+/-few ms) it may activate two channels etc.

author: Paul Price
author_rank: Super Contributor
timestamp: May 16, 2014, 04:03:49 pm
content: This works for up to15V Power Supply.Only one push-button switch selected power supply will be activated at any time.This design may be easily expanded to any number of select switches you like.The unused second D Flip Flop pins for D, Cp, S, and R need to be grounded.

author: Tim K
author_rank: Newbie
timestamp: May 16, 2014, 11:32:56 pm
content: Thanks. Those are both very helpful. I have some CD4049's. Would those work or are they completely different? Doktor Pyta, what is the circuit fragment inside the box on the right side of the schematic?I had an amplifier years ago that probably had a similar switching circuit. I had to replace the chip a couple of times because it was being damaged whenever the foot switch cable was loose. I'm assuming a simple zener diode would prevent the same thing from happening this time, but I was hoping to avoid IC's altogether. Is there any way to accomplish this using MOSFETs?

author: Paul Price
author_rank: Super Contributor
timestamp: May 17, 2014, 01:20:29 am
content: If 4013's are apples, 4049's are anteaters.You can foot your switch, but you can't switch 4013's with 49'ers without getting the boot.P-Chan Power MOSFETs can be used in place of the 2N3906's.Frankly, I can't see the logic in eliminating IC's.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: May 17, 2014, 08:28:19 am
content: Quote from: Tim K on May 16, 2014, 11:32:56 pmIt is the monostable multivibrator which produces a latch pulse few milliseconds after pressing a button.But IMO Paul's idea is better.It basically uses RS flip flops (made of D type), so influence of timing and contacts bouncing is reduced.

author: Paul Price
author_rank: Super Contributor
timestamp: May 17, 2014, 01:06:38 pm
content: There is "no contact bouncing is reduced.." with my circuit. No contact bounce effect at all.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: May 17, 2014, 03:14:01 pm
content: Quote from: Paul Price on May 17, 2014, 01:06:38 pmTrue.That's what I meant to say.

author: Tim K
author_rank: Newbie
timestamp: May 17, 2014, 03:27:29 pm
content: Okay. I'll give it a try. Is there a quad version of the 4013?

author: Rufus
author_rank: Super Contributor
timestamp: May 17, 2014, 04:27:35 pm
content: Or much simpler and a little crude the attached.One of the 3 outputs will be low. A small capacitor across one of the push buttons would set the active output on power up.Pressing multiple buttons activates multiple outputs - if that is an issue all solutions will be more complicated.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: May 17, 2014, 06:14:29 pm
content: Now....This is brilliant!!!