If I want to figure out options in power, gotta know what the circuit in theory would draw in current. Which meant a lot of datasheet reading and some napkin calculations to get a rough idea..

LOGIC Power Draw

Logic power consumption tends to be based on activity like clock speed. For most of the logic. The clock-speed is anywhere between 2hz for frequency divider and ~0.00003hz. For these it is safe to assume their consumption is just the Quiscent Current and IO to other logic. Which is between ~4-10 uA

The 4060 is a little costlier as this one will have a 32Khz clock as an input. There is no exact way to calculate the current, so instead I am noting down the listed maximum Icc of 80uA.

Tallying up the 9 ICs and being a little conservative. I would expect a power draw around 150uA or 0.15mA. That is very cheap in power.

Calculating LED power consumption

Leds are complicated, they are constantly switching and there is a notable difference in efficiency between various types of Leds and various sizes. For starters I wanted to figure out how much is consumed on average.

I mapped out how many leds are on for any Binary Coded Decimal and from this calculated how many leds are on on average per clock digit. Before finally combining them to get a total average number of leds on per day for a full display and a Peak:

Calculation indicates anywhere between 0 and 14 being active at any time with an average of ~7.5 for the entire clock. This average not accounting for how the last two digits are cut off by lasting 24 instead of 30. But it’s better to overestimate than underestimate. The most leds that can be on at the same time are 14.

Choosing a led

Leds are a nightmare to shop for as few leds are the same. Some are more efficient than others. Example: My OSRAM Yellow and red 2V leds are still quite bright at a mere 0.45mA. But the green leds need at least 1mA to be visible. This being mostly because of the material used to actually get the coloured light.

To choose an efficient led one must look at current and millicandela. Most modern leds have a almost linear relationship between current and millicandela (mcd) output. A led with higher mcd compared to the current going in, has a greater efficiency and if you got a target mcd in mind you can estimate how much current you need to get to it.

From some quick testing of my owned leds i find that i would need ~3-7mcd from any led to be visible. Depending on colours.

Since I am building three of these clocks. I’m going to be planting a variety of different colours in 1206 format. One I will give Red,Yellow,Orange leds, the second Violet and the third I was thinking green. Kingbright got a nice set of options in their APT series and if calculations are correct, they can be powered at anywhere between 0.5 and 1mA. I put down rough estimates below.

Notable is how there are a few that seem to be insanely efficient. Something i will want to verify properly once i order them all.

Small note on Forward Voltage

The Forward Voltage drop of a diode is not a constant. It too depends a great deal on the current passing through it. The rated forward voltage is that at nominal current, but if you go below the rated current the forward voltage also starts to drop. For example most standard leds have a forward voltage either around the 2V or the 3.2V. But if you are going for as little current as i am, then the fV is more around the 1.8 and 2.6V.

This is very important to keep in mind when testing and calculating Resistance.

Total Power

Using the average per day. Leds are expected to consume anywhere between 1mA to a max of i'd say 7mA (rounding up a lot). While the logic is expect to be about 0.15mA.

This clock should be crazy efficient using no more than 10mA. With the main consumer being the leds themselves. This opens some possibilities in how to power it (next step).