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Ever wish you could tie two 2P4T rotary switches together so they work in synch – and do it with a single stompswitch? Or maybe even just be able to use a single stompswitch to step-thru 1 of 4 selection options for circuit switching? Or how about the flexibility of both in one circuit with two separate stompswitches?
Well, here’s a dual 1-to-4 sequential analog switching circuit with two sequentially synchronized 2P4T switches and a single sequential 2P4T switch. Based in CMOS logic components, instead of an MPU like an Arduino, this is a dedicated discrete logic solution. Using a standard CD4011 as a dual debounce circuit for two mechanical momentary-on stompswitches, two CD4027 flip-flops set up as 2-bit counters, and a few CD4052 analog switches. I’ve breadboarded it three times, left it on for hours at a time and intermittently tested it a lot to ensure it works.
Essentially, it does the work of two synchronized 2P4T rotary switches and a separate single 2P4T rotary switch. Both are actuated by a single momentary-on stompswitch. No more reaching down to turn a rotary switch.
The idea came to me when trying to find a means turn a strangely wired pair of slider switches into a user interface that allows a stompswitch to change the selection. In this case, the selections are 1, 2, 3 or 4.<span class=”Apple-converted-space”> </span>And the signal ins and outs are left completely to the builder’s discretion. The usage potential is enormous and with the CD4051 or CD4053 analog switches, (and some modified logic circuitry), other sequentially operated switching configurations are possible. And no MPUs to program.
The schematic . . . .
And here’s a photo of the breadboard testing rig. (I plugged my Strat into a Rockman X100, the X100 into one of the analog input lines of the CD4052 and the output of the corresponding analog line into an amp. And moved the I/O connections to each of the CD4052 I/O lines to test that the selector and corresponding LED indicator would light and remain in synch with the selected option.) I powered the Rockman and the breadboard with those two small DC-DC Buck Converter modules with a simple negative center, 2.1mm, 9v DC wall wart.
The power supply is a pair of cheap Chinese Buck Converter modules wired to deliver the ±6v dual rail supply and just tapped of the +9v input to supply the CD4011 & CD4027 logic chips. I had to test several different Buck Converter modules to find ones that would allow an unconventional wiring to provide both positive 6v and negative 6v from a single common +9v supply. I found one particular Buck Converter that uses the MP1584EN smart-chip that will do this. Several other smart-chips I tried would NOT invert the polarity of its output. Here’s a diagram showing the DC-DC Buck Converters that work.
If you’re interested in trying out the MP1584EN DC-DC Buck Converter yourself (they have wide range on supply and output options, a high operating frequency [~1m Hz], low ripple [~30mv], better current output than most any chargepump, and are cheap), I found two sources and have tried them both – and they work.
Amazon: MP1584EN-DC-DC-Converter-Adjustable-Module
and eBay: MP1584EN-DC-DC-Converter-Adjustable-Module
Anyway, there’s my “Switching Post” for the day.
This is really interesting! Have you had any noise issues with the converters?
Do you have a particular application in mind for the SSU?
Thanks for sharing!
Fig – I’ve had no noise issues with these converters. As part of standard operating practices, I did add a 1µH coil, a 47µF electrolytic and a 100nF ceramic cap at the converter outputs.
Apologies, I see that in the notes now. Really cool!
Would it also work if you used a 7660S to provide both +9V and -9V and then use 78L05s to drop the voltages? Would it work with 5V? Just wondering.
I love the switching idea.
Wilkie1 – Of course. Charge pumps can be used to create a dual-rail supply. However, they are far more limited in the amount of voltage & current they can supply. These BC modules will deliver up to 20v (max) @ 3A (max). Ohm’s law applies to the voltage/current ratio.
This particular BC module is a “step-down” converter and requires that the supply be ~2v higher than the expected output. There are other “step-up” BC converters that can deliver a higher voltage than fed into it. But the ones I’ve tested will NOT deliver a reverse polarity voltage when wired as shown in the initial post. The battery got very warm.
The idea was to come up with a dual-rail supply that can use a standard 9v inout (like DC bricks and/or wall-warts) and deliver a dual-rail supply that drive not only the switching circuit, but a Rockman X100 as well. The Rockman X100 calls for ±6v dual rails at ~200mA. The switching shown above, is the generic version of the switching matrix I designed to replace the two slider switches in the Rockman X100. The X100 has two double bladed slider switches that are rather oddly configured. One selects the MODE and requires two CD4052 analog switches to emulate. The other switch can be emulated with a single CD4052 analog switch. Here’s the schematic of just the two switches that the above circuit can emulate (the “A”, “B”, “C” & “D” references are artifacts from the design work done for the X100 switching circuit):
The whole thing started when I decided I wanted to rehouse the Rockman X100 into a pedal enclosure. I spent a few of weeks researching and sorting it all out.
Ah so! Now I understand the whole picture. Well done!
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