Ideas for emulating a mechanical 24 hour time switch?

[e100]

The kind where you have a circular dial that has 96 (4 per hour) pull up or push down switches that slowly rotate past a microswitch every 24 hours.
This old style user interface design is much easier to use than the modern push button interfaces with an LCD display where you have to press multiple buttons to see what programs have been set.
The disadvantage is that they lose sync with real time if they lose power and the clock mechanism wears out after a few years.

Connecting 96 electrical switches to a micro would be an expensive time consuming process. 0.1" jumpers get lost and dip switches are too fiddly for normal sized fingers.
Ideas anyone?

[helius]

pushbutton dial encoder + good minimal UI on a Memory LCD or poststamp VFD.
UI flow: rotate encoder to highlight current time, instant on/off (default selection), or schedule. Schedule is a pie chart with 24 hours, and is programmed by aiming encoder at x hour, then pressing to select on or off. spinning encoder deploys on (or off) setting to adjacent hours to x. Holding encoder down for .75 seconds exits programming and displays on/off schedule.

[Brumby]

I really like that rotary encoder idea.

You could explore other display options as well.

[james_s]

That's exactly what I was going to suggest, encoder and a circle of LEDs, you beat me to it. You could charlieplex the LEDs if you want to get fancy and probably get by with a modest microcontroller. DS3231 RTC for timekeeping with a lithium coin cell to hold the time over a power loss. 

[BradC]

The disadvantage is that they lose sync with real time if they lose power and the clock mechanism wears out after a few years.

Oddly enough I've several 24 hour electro-mechanical timers that are well in excess of 15 years old, keep time if they lose power (they have a ni-cd backup), and are still functioning perfectly (even on their original ni-cd cells). I have 2 electro-mechanical timers from the days before they had built-in backup that are pushing 40 now and still perfectly functional. In fact, I've _never_ had to replace an electro-mechanical time clock, although I did need to repair a microswitch in one a few years ago.

I've had to replace several devices with solid-state timers in that time. So my experience is directly counter to your reliabilty assessment.

[james_s]

How does the electromechanical timer keep time with a battery backup? Every one that I've ever seen is driven by a synchronous motor that requires AC to run.

I've had several similar timers fail. Usually one of the gears cracks, a couple times the lubrication in the motor has gummed up, one of those I was able to revive by soaking the motor in some machine oil.

[SeanB]

Battery backed uses a standard CMOS 1V5 clock chip, 32kHz crystal and coil to drive the mechanism. The incoming mains is applied to a 1N4007, a 100k series resistor and then the chip is connected across the single cell NimH cell and a green led for protection when the battery goes open circuit. The 1Hz tick drives a standard set of clock gears to run the setting drum.

[james_s]

That's interesting, I've never seen a timer like that in the US. Perhaps they're out there and I haven't been paying attention, or maybe it's just one of those things we've always done differently.

[GoneTomorrow]

I have one of the battery backed up ones too. When I first used it I thought it was busted because the battery was completely flat and must have been pulling the internal supply way down. It started sticking after being powered for a couple of hours. They're really nice for permanent installations (diesel furnace in this case).

I also have a non-backed up one from like 1982 that has been used since then for controlling water pumps, and it's not worn out yet.

[Brumby]

.... encoder and a circle of LEDs ...

Yeah ... that's what was floating around in my mind too.

[Ian.M]

Annular slider touch sensor with a ring of reverse mount SMD bicolour LEDs just inside it, + a few touch buttons and status LEDs in the middle?

Actually DIP switches aren't much more fiddly than the operating levers on a mechanical timer.  Use a ring of rocker or side lever actuator 4 way ones.   The problem then becomes displaying and setting the current time effectively.  For that, one could use a tiny 96 step/turn stepper motor, driving a pointer disk with a Grey code absolute encoder pattern on the underside.  Normally the MCU rotates it one step every 15 minutes, but the user can manually turn it to a new time and the MCU uses the encoder to read back its position to know which switch to check.   However its certainly going to be *FAR* more expensive than a plastic mechanical timeswitch!

[ebclr]

[Seekonk]

Just what exactly is the purpose of this time switch?  If it is for home security, I would use a micro that tracks daylight and turns things on and off in a pattern that is not predictable.  For other operations it is not likely that 96 positions are needed, likely only 6 to 12 actual times where things change.

[Codebird]

More cool than practical, but...

1. Rotating disc. Physical disk. Divided into segments for easier counting of quarter-hours.
2. Infrared reflective sensor pressed up against disk.
3. Pencil with which to fill in the boxes of the times you want it turned off.

If you are 'emulating' mechanics then why not just emulate with mechanics? If you use a stepper motor to drive then you have it down to exactly one moving part.

[calexanian]

Do you want it to turn? I don't have a clear idea of implementation but a motorized potentiometer came to mind. map out the sweep of the resistor and run the motor to certain spots to emulate the spin of the clock or something.

[Ian.M]

I think I like the idea of a disk directly driven by a 96 step stepper motor driven with a row of little radial sliders round the edge of it and a fixed reflective optosensor at the 12o-clock position to detect if the current slider is in or out.  The U.I  would be *exactly* equivalent to the mechanical timer, and all the electronics has to do is pulse the stepper once every 15 mins and drive the relay from the optosensor output, but its still eliminated nearly all the parts that wear out on the fully mechanical original.

Otherwise, what about a single button, single LED interface? push on, push off, hold 15 secs to pair with a master controller via a powerline data protocol.  The master could have a full U.I. or it could be controlled by an Android device (or PC) running an app that can be used to program the timers, or fully IOT enabled.  The timers would each have their own RTC so would be autonomous if they loose comms with the master.