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Need schematic: 60-LED analog seconds-only clock Answered

I built a "barn-door" tracker to take photos of planets and stars so that they are tracked (i.e they appear as dots, not trails). See http://en.wikipedia.org/wiki/Barn_door_tracker if you want more info about  trackers of this type.

My tracker can be seen in the first two photos here: http://www.tjimaging.com/ted/astro.htm

These devices depend upon the user manually turning a knob at exactly one rpm for as many as fifteen minutes. This is (very) tedious, but gets good results. The biggest difficulty is in keeping the proper rate of knob-turning. I use a stopwatch timer and have a pointer on the knob so I can manually match each second as it goes by. This has to be done in the *dark*, though, for obvious reasons! So there's an additional problem of lighting the dial and stopwatch.

My idea would be to affix a steady red LED to the end of the knob pointer and to use an analog clock consisting of 60 red LEDs arranged in a circle around the knob. Only one LED would be lit at a time, starting at 12 o'clock position, and advancing one LED at a time, clockwise, and keeping each LED lit for one second. This arrangement would let me simply match the knob's steady LED with the currently-lit one and thus makes manual matching of the "second hand" visually easy.

I expect a 555 timer circuit (powered by battery, not A/C, for portability) could handle this task, but I don't know enough about electronics to know for sure. I'd like to keep the cost lower than it would be if an Arduino-based circuit were used.

I've also never made a custom printed circuit board, but I'm game to try after building a successful breadboard.

I just need a schematic!  Thanks, all.


I used to make drivers for these things commercially, with little battery operated AC motors, that ran off a crystal - they'd run for a week on 4 AAs

@steveastrouk: I'm aware of the motor-driven versions, but for this project I want a manually-driven system. Thanks, though!

Well, are you happy to use a microcontroller ? I have a solution for you if you can.


I'd like to make the simplest and least expensive system that will do the job. If a microcontroller fills that bill, then yes! But I don't know enough to say myself yet.

Well, I have a two chip solution for you, and I may even throw in a PCB design - it was an intriguing problem to lay out all the LEDs in a nice circle as an exercise !


Wow, that's great--thanks! What diameter did you use for the LED circle?


OK; so how can I see what you have in mind? Am I missing a link you posted to your design?
Thanks in advance1

Here it is so far, its pretty well complete, apart from the wiring of the ATtiny168 at its heart. The idea is that the centre of the board is completely clear of wiring, and there's a 9/16 hole in the centre. I shall write it up and enter it into the competition I think.


Wow, that's beautiful! I'm eager to see your final version.

I'm toying with which processor to use on it at the moment, I started laying it out with Arduino, then changed my mind.

I think I've given you enough time to decide (5 years)--any current thoughts? :-) :-)

He He. Lots happened in the interim. I emigrated to the USA for a start.

I was only looking at the PCB a couple of weeks ago, and thinking of making it.

look up the 4017 chip, cascading 6 plus something like a 555 timer should do exactly what you want. Instead of a 555 timer, I recommend taking apart a clock that runs off of 1 AA battery and get the little circuit board and attach 2 diodes to it for a 1hz signal generator which you can then input into the 4017 chips.

4017 tutorial:

I cant seem to find a link to how to make the pcb in a wall clock work with a setup like this. but if I remember correctly all you need to do is take the 2 pads the coil (solenoid motor what ever) was connected to the pcb and connect the anode of a diode (such as a 1n4148) to each pad. You need to diodes, and attach the anode of one to one pad and the anode of the other to the other pad. then connect the 2 diode's cathodes together, the 2 cathode connection is where the 1hz signal is.

Thank you! I'll look at the website and ponder your comment. I don't know how to "cascade" the six 4017 chips, but maybe I can figure that out.

Heres a schematic which is pretty minimal: The transistors are only necessary to invert the signal (a 2n3904 or 2n2222 will work fine). The base resistors to the transistors could be 10k (pretty much any value from 1k to 10k will work, the value isn't that important). the resistor for the leds should be like 470 ohms, but that really depends on your power supply. The only thing not shown in the schematic is all of the leds. You will have 6 sets of 10 leds (see schematic, connect all cathodes and put a resistor on that cathode). for each set, attach all "LED1" together, all "LED2" together, etc. So when all of the leds are connected you will have 10 anodes and 6 cathodes. attach the cathodes (through the led resistor) to each transistor. Idk if im being clear with this, but feel free to ask questions about it

4017 example.png

how do i connect the next set of leds.plz help..

Cool! Thanks--I'll take some time tonight to see if I can understand this.