Inside a TM623 astronomical time switch. (self adjusting to season)

Unlike traditional fixed time time-switches an astronomical clock adjusts the programmed switching times according to your location on the planet and the time of year. That means the lights will come on progressively earlier in the darker nights and then later in the brighter part of the year.

Most of the work is done by a standard module with the base circuitry dealing with power and switching.
The design is a bit quirky. It seems to use a higher voltage zener (36V) to give the 24V relay a boost before the voltage drops to about 21V when it's on. The 330nF X2 capacitor could be swapped for a 680nF one for 110V use.
The hot zener is directly next to the smoothing capacitor, which is a design taboo.
Another design oddity is the relay coil being on the emitter of an NPN transistor instead of the collector. And the reset circuit is just extreme!

I've now done a timing test and this unit gains by about a minute a month.

Here's a guide on how to program this type of switch:-

Press the MD and R buttons (two left hand ones) together to enter latitude and date setting mode.
Use the shift (middle) button to select latitude and then the up/down buttons to adjust.
You can find your latitude by searching on google.
Once the number is set press the shift (middle) button again and then you can adjust N or S (north or south) with the up/down buttons.
Press the shift (middle) button again to finish.

While in the same mode (or by pressing both left buttons again) you can set the date by pressing the mode (left hand) button. Pressing the shift (middle) button will step through day, month and year allowing them to be adjusted up and down. Press shift (middle) again to finish.
Unit will revert back to a normal locked display after a delay.

To set the time and switching settings hold down the mode (left) button continuously for about three seconds until the word "lock" disappears from the screen.
Pressing the shift (middle) button will step through minutes, hours and seconds, allowing them to be adjusted up and down. Press shift (middle) button again to finish.
You can then set the switching times or leave the unit until it locks again.

To set the switching times unlock the unit if it's still locked by holding down the mode (left) button for about three seconds until the work "lock" disappears.
Press the mode (left) button to step through the programmed times. You can also step forward or backwards using the up/down buttons. There are eight on and off times available. The first on and off will have automatically been set to a typical street lighting or signage time, coming on at dusk and turning off just after midnight.

When you are at a time you want to set, press the shift (middle) button to set the time.
First the minutes flash and can be adjusted, then when the shift (middle) button is pressed the hours will flash and can be set.
The next press of shift (middle) will cause both hours and minutes to flash and you can choose whether it's a self dusk adjusting time or if it's a fixed on/off time by pressing up/down. When the little circle/planet appears it is self adjusting to dusk throughout the year.
Press shift (middle) once again to exit that time setting and then increment to the next one by either pressing the mode (left) button or up/down buttons.

You can delete an unwanted setting by pressing the "R" button (second left).

Once finished, the unit will revert to a locked state after a delay.

To set the output on, off or auto press the two outer buttons (mode and up-arrow) to cycle through:-
ON - Output is on continuously.
ON AUTO - Output is on, but will change with programmed time settings.
OFF - Output is off continuously. (Do not use as a means of circuit isolation.)
OFF AUTO - Output is off, but will change with programmed time settings.

To reset the unit completely, short the terminals marked 3 and 4. If powered they will be live at mains voltage. It's better to do it with the power off. It will effectively short the internal battery and cause the unit to reboot.

The unit has a 3V lithium cell that is trickle charged when the output relay is on.

You can check the cell state by powering the unit down and measuring the DC voltage across pins 3 and 4. It should be in the region of 3V.

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