First get a clock (I got mine at a reasonable price from a charity shop).
The clocks all have similar electronics/mechanics. The moving part is a strange type of shaded pole motor (or perhaps more correctly a single phase stepper) it is known as a Lavet-type stepping motor.
To step them each pulse is the reverse polarity of the previous one.
The first problem is the clock electronics produce a perfect square pulse (really perfect!) (even with the inductor connected) this is something I could not manage.
The trick was to make the pulse long (the clock produces 32 ms pulses) I used 100 ms with a 5 ms reverse pulse at the end (probably this was not needed, but belt and braces). I used 3 outputs on the PIC and no back EMF protection.
Next problem is the clock normally runs off 1AA battery and to power the PIC I need two. So the solution is to centre tap the two AA batteries. This quite nicely gives an easy way to reverse the polarity.
So have the pins set on for the first pulse and off for the next, in between set them as inputs.
Now for the timing - remove the hour hand. The minute hand is going to indicate the tide phase.
The tides move in mysterious ways, but on average high tides are separated by 12 hr 25.2 min. The second ticks will now have to be 12.42 sec (approx).
What I did was use a standard 32768 Hz crystal fed into a 16-bit counter with the prescaler set to 8:1. So the counter overflows every 16 sec, but if you intialize the counter with TMR0H=57, and TMR0L=70 the overflow will come in 12.42 sec.
At one stage I did look into correcting for the influence of the sun, but it proved too difficult. Much of the problem is that the British admiralty "own" the tides and (despite using tax payers money) will not reveal the tide components and phase. In fact there are programs that can be downloaded to predict tides and all the UK data has had to be removed (not so for other regions of the world).
Anyway it is like my normal clock which shows mean solar time, this one shows mean lunar time. Here's a picture showing just after low tide (6 is low 12 is high).
I should have mentioned, if you are tempted to try this, taking apart the clock mechanism is tricky.
Do it gently as you are going to have to put the gears back and need to note where each one goes.
Putting it back together be careful not to bend the top of the gears (I've done it and just about got away with it).
You may think I was over dramatic in saying tides move in mysterious ways , but I was traveling along the east Anglia coast on Tuesday. I started at Felixstowe and went to Cromer. The tides were quite different. So I looked them up and they are more than 5 hours out of phase. How does that work they are not that far apart (in global terms) and they are both on the north sea?
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First get a clock (I got mine at a reasonable price from a charity shop).
The clocks all have similar electronics/mechanics. The moving part is a strange type of shaded pole motor (or perhaps more correctly a single phase stepper) it is known as a Lavet-type stepping motor.
To step them each pulse is the reverse polarity of the previous one.
The first problem is the clock electronics produce a perfect square pulse (really perfect!) (even with the inductor connected) this is something I could not manage.
The trick was to make the pulse long (the clock produces 32 ms pulses) I used 100 ms with a 5 ms reverse pulse at the end (probably this was not needed, but belt and braces). I used 3 outputs on the PIC and no back EMF protection.
Next problem is the clock normally runs off 1AA battery and to power the PIC I need two. So the solution is to centre tap the two AA batteries. This quite nicely gives an easy way to reverse the polarity.
So have the pins set on for the first pulse and off for the next, in between set them as inputs.
Now for the timing - remove the hour hand. The minute hand is going to indicate the tide phase.
The tides move in mysterious ways, but on average high tides are separated by 12 hr 25.2 min. The second ticks will now have to be 12.42 sec (approx).
What I did was use a standard 32768 Hz crystal fed into a 16-bit counter with the prescaler set to 8:1. So the counter overflows every 16 sec, but if you intialize the counter with TMR0H=57, and TMR0L=70 the overflow will come in 12.42 sec.
At one stage I did look into correcting for the influence of the sun, but it proved too difficult. Much of the problem is that the British admiralty "own" the tides and (despite using tax payers money) will not reveal the tide components and phase. In fact there are programs that can be downloaded to predict tides and all the UK data has had to be removed (not so for other regions of the world).
Anyway it is like my normal clock which shows mean solar time, this one shows mean lunar time. Here's a picture showing just after low tide (6 is low 12 is high).
Last edit: David Stephenson 2022-06-13
Thanks for that.
I'm looking into the feasability of making a Moon phase "clock". I may use some of your inspiration to derive that from.
I should have mentioned, if you are tempted to try this, taking apart the clock mechanism is tricky.
Do it gently as you are going to have to put the gears back and need to note where each one goes.
Putting it back together be careful not to bend the top of the gears (I've done it and just about got away with it).
You may think I was over dramatic in saying tides move in mysterious ways , but I was traveling along the east Anglia coast on Tuesday. I started at Felixstowe and went to Cromer. The tides were quite different. So I looked them up and they are more than 5 hours out of phase. How does that work they are not that far apart (in global terms) and they are both on the north sea?