1
\$\begingroup\$

I would like to build a control panel to direct K power sources to N loads. A power source can control any number of loads, but a load can only be connected to a single power source. Each power source is variable (0 to 16V at up to 2A).

In a purely mechanical version, I imagine using a K+1 rotary switch for each load, where "+1" represents a no-power-source state.

I would like to implement this with a minimal set of small pushbuttons. I imagine a multiplex-like setup of pushbuttons as follows: each power source is represented by a pushbutton; each load is represented by a pushbutton. When a pair of pushbuttons(source,load) is pressed, the load is powered by source.

I've put together a circuit with AND gates to represent each pushbutton(source,load) combination; latches to hold state; and a grid of transistors to connect variable power sources (P1, P2, ..) to loads (targets 1, 2, ..). A separate constant power source Pc is used for the circuitry.

Design proposal for circuit to control K power sources to N loads

Missing from the diagram is reset logic which would ensure that at most one power source is connected to a load. Also missing is logic for the no-power-to-load option, which I imagine could be a P(zero) pushbutton.

I am seeking input to this design. Am I missing something substantial? Have I oversimplified the problem? Working with multiple power sources, does this circuit create undesired effects?

Thank you.

\$\endgroup\$
2
  • \$\begingroup\$ Is there a reason you wish to do this with discrete parts? \$\endgroup\$ – ThreePhaseEel Aug 21 '17 at 2:15
  • \$\begingroup\$ No particular reason beyond that this is all I could think of. What alternative do you have in mind? A design choice I'd like to stay away from is PICs and other software-based solutions, primarily because I feel that such solution is overly complex for what I consider to be a mundane switching problem. \$\endgroup\$ – Cosmo Jetz Aug 22 '17 at 17:10
0
\$\begingroup\$

First, I don't think you need source buttons, but eliminating them actually increases the number of buttons. What you have is a SSAD (Source Select At Destination) routing switcher, but for power instead of video or audio.

For a 4x4 array, each output has 4 buttons, one for each input. Pressing any button latches 4 bits, and since only one button is pressed at a time, the latch for that output line holds one 1 and three 0s. If the latch outputs are negative-true, then PNP power transistors will make efficient high-side switches.

With only 8 switches, the latch input becomes a bit more complex.

\$\endgroup\$
1
  • \$\begingroup\$ Thanks. I see from another post of yours that you're referring to the 74HC/HCT259 8-bit addressable latch. IIUC, this would replace the LATCH section in my diagram, considering that I retain the (source,load) pair of buttons and the AND gates in section INPUT. Using this 8-bit addressable latch would solve the single-output portion of the design problem. To clarify, does HCT259 work with momentary inputs (such as a pushbutton) while retaining state (pushbutton depressed)? \$\endgroup\$ – Cosmo Jetz Aug 22 '17 at 17:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.