AXT Systems

Power Sequencer
Power Sequencer
If you regularly have to power up equipment in a particular order ( eg preamps, console, power amps) and power down in the reverse order and want to do it with the press of a single button then this unit may provide the answer.

The 4-channel power sequencer unit is a simple module which will drive 4 relays in sequence with a 1.5s gap between each. The sequence is initiated by pressing a 'start' button and the sequence operation is determined by the position of the UP/DOWN switch.

Operation is simple. Flick the switch to 'UP' and press the start button and the unit will power UP the 4 realys in the sequence 1-2-3-4. Leave the switch in the UP position and any subsequent button presses will not do anything, since it is already powered up. This is handy to prevent accidental bumping of the start button from powering down at the wrong moment. When finished for the day, flick the switch to the DOWN position and press the start button to power everything DOWN, in the sequence 4-3-2-1.

I use one of these in the studio, to power up and down preamps, console and speakers in the right order. The power switching box is separated from the control box by a control cable, allowing the control box to sit on the desk taking up minimal room and the power switch box on the floor behind the desk.
The control box contains a small module with a PIC16F628 microcontroller on it, configured to read 4 active low inputs and control 4 open collector transistor outputs. It is powered from 12VDC and has an on-board regulator to generate the 5V rail. A link allows the 12V input power to also power the relay modules (if 12V relays are used in the power box), otherwise a separate relay excitation power input is provided.

The power switch box contains 4 power relay modules, each one controlling power to a double GPO. There's a fuse-protected IEC connector for the mains into this box, so total power should not exceed the IEC lead rating in this configuration. A locking 5-pin DIN connector was used for the control cabling between the boxes, but any 5-pin connector could be used. A later version of the power box simply had four 4-way power boards wired to a smaller box with relay modules inside, which was a more convenient arrangement for studion power sequencing.

Circuit diagram, PCB, firmware source and BOM are shown in the accompanying PDF files. An assembly diagram shows the connections and separation of controller and power switches.

The firmware is written in C and can be compiled using the free Microchip MPLABX IDE. A hex file is also included for the firmware which can be simply programmed into the PIC16F628 device without having to compile the source code.
Power Sequencer
PSEQM-1 Control Module-top view
Power Sequencer
PSEQM-1 Control Module-bottom view