Battery Lifespan

Nothing wrong with putting an Arduino Uno to sleep provided James' clock doesn't need it to be awake for some other reason. The other downside is learning to program sleep modes; they aren't the best place for a beginner to start.

The Uno is my favourite Arduino; I brook no criticism - it is the best of all possible Microcontroller boards!

Even so I have to admit that power efficiency isn't a top Uno virtue. It might suit James to use a Nano or one of the other alternatives. A raw Nano consumes about 20mA compared with a Uno's 50mA. And of course a Nano also has sleep modes, and it's possible to take other measures to reduce power consumption such as chopping out the LEDs (2mA). Might also be fun to see how much you can reduce the chip's input voltage below 5V before the Arduino crashes. Reducing voltage will also reduce the current consumption.  (You can bypass the on-board regulator by applying power to the Vin pin.)

Dave

Edited By SillyOldDuffer on 03/04/2018 10:33:10

This reminds me of my millstone project years ago, an electronic cat flap. Leaving aside all the excitement of how you detect a specific cat and why a US submarine communications system interfered with it when the flaps were aligned north/south, the initial design (not mine) had a solenoid that pulled out a pin that locked the door when the right cat was detected. Problem, when cat was in hurry and pushing on the door, the friction on the locking pin was increased, solenoid didn't have enough grunt to pull it free especially when batteries were low.

The initial solution was to operate the lock through a knee joint, under slight pressure, with the solenoid giving it a "kick" behind the "kneecap" to release. This worked better because the solenoid has a chance to get up some wellie before it was called on to do some work, but still occasionally misbehaved. But many thousands were supplied and worked well enough. But the solenoid was probably the single most expensive component in the whole thing.

I managed to leave that company before a Mark II was developed, but when it was they used a little DC motor working a worm. Much better performance, used much less current, cost peanuts because motors are made by the millions unlike solenoids.

Do solar panels work off interior lighting? If so rig one up to charge the clock battery, or put the clock near a window.

About as well as a wind turbine on a car roof!

Actually, there is a solar charged clock in Buckinham Palace. As fa as I know, it is still there. I know one of the designers involved with the project.

Or just build a sundial.

Or use a raw AVR chip and get the average consumption down to less than the battery self-discharge by using deep sleep modes

LTD Stirling engine on top of a radiator?

Well according to **LINK**

a turbine with an area of 1 sq ft attached to a car doing 30 mph would generate about 50watts, so unless the OP's clock is particularly heavy on the electricity he will be well in!

You can get solar powered watches which use solar power to keep the battery charged.

**LINK**

Thank you, again, for the ideas and suggestions. I shall have a look at the Nano, as suggested. I have the Uno simply because it was a present, rather than by active choice.

I am going to try a practical test to get some idea of likely battery life span. I have the Uno wired up to a LCD clock display and LEDs flashing instead of solenoids operating: as an interim I plan to buy some small three volt relays to replace the LEDs as I hope that these will approximate more to the current draw of a small, three volt solenoid. I shall then run it from six C cells and see how long it lasts. I can also use my multi-meter to measure current usage.

I have plenty of time to test it as I am still working on the actual clock mechanism's design.

Regards,

James.

Good morning.

Last night, I set up my Uno and clock circuitry to run on six alkaline C cells. I measured the current draw: 60 milliamps when only the LCD was running, rising to 150 milliamps when a LED triggered. Disconnecting the LCD, which is only used to set the time, reduced the draw by a couple of milliamps.

By my estimation, this will give me a running time of about five and a half days at the outside for just the resting circuit. Add in the additional drain for all of the LEDs (currently one per second, minute, hour, am or pm indicator, day of the weeks indicator and two for the quarter and hourly strikes and chimes), and I shall be lucky to see a few days before the batteries go flat. I used the LEDs, which will be replaced in time with the solenoids, to test my progamming, Oh, well, time will tell.

Somehow, I think that I shall need to use an external power supply after all, reserving a small nine volt battery as a back up, should the mains become disconnected.

Regards,

James.

Edited By James Alford on 05/04/2018 07:25:05

James, one of your problems is that you are supplying the UNO board with 9v which it drops down to 5 v using a linear regulator (assuming your cells are in series). Almost half the energy of the batteries is being wasted as heat in the regulator. So actually all the battery voltage of 6 cells above about 6v which is probably the drop out voltage of the regulator is doing nothing for you. If you want to benefit from the extra cells you need to have a switched mode regulator, a buck converter in the jargon, that effectively transforms the voltage down and the current up, so reducing your current drain from 60 down to 40 mA.

Yes, a buck converter is an alternative to the standard linear regulator. To apply to the Arduino, you use one of the other power inputs that bypasses the on-board regulator.

A buck converter circuit using a standard chip from TI that costs £1.20 from RS is described here. The description isn't very good because it omits the key point, which is that an inductor is in effect used to drop the voltage which can give very high efficiency. You can probably also buy ready-made converters if you look around the web.

These are key components in modern electronics - for example in a mobile phone the LiPO battery gives around 4V but several of the ICs run on ~1.8V, so the 2.2 V difference has to be dropped as efficiently as possible to maximise battery life. This means that a lot of development has gone into making the chips as efficient and cheap as possible, and simple to use.

Yes, 'buck converter' is a better, but more complicated/expensive way of regulating power.

A downside of the Arduino Uno is that it's designed to 'keep it simple' for beginners, and that includes simplistic advice about how best to power it. Sensible and safe. Actually there are a number of possibilities.

It's a 5V board. You can power it with a USB cable from a computer or a wall-wart charger. (USB is 5V). Or feed it 5V from an external stabilised power supply through the Vin Pin. Or feed it 6 to 20Vdc rubbish through the power socket.

As John says the Uno's power socket input uses a linear regulator to burn off excess volts, which is very inefficient if the device is being powered by a battery. To avoid overheating and voltage drop-out problems Arduino recommend keeping the power socket input voltage between 7 and 12V well within the absolute range which is 6V to 20V.

However, whenever I battery power a Arduino I use a 6V accumulator like this example. Although below the 7V recommendation it works. I have to keep an eye on it though: one day I might plug in a Uno and find its regulator blips out on only 6V causing crashes etc.

The more advanced Arduino M0 uses a switch mode regulator that doesn't burn excess volts. It only requires 20mA while being 3 or 4 times faster than a Uno, with massively more memory and several other tasty features. Don't get too excited though, the price for the goodies is that it uses 3.3V logic and the input-output pins are comparatively under-powered and delicate. In other words it's much easier to blow up!

Something wrong if turning on a LED causes the current to rise to 160mA. I suspect a short-circuit. The maximum current provided by a single output pin is 40mA (20mA recommended) and a small LED might draw between 2 and 10mA. Are you switching the LED with a transistor? If so don't forget that, unlike a solenoid, the LED will need a dropper resistor to limit the current. (Try 330 - 1500 ohms)

Dave

I had forgotten about my old watch

Seiko solar watches seem to go on forever kinda thing nowadays, they use some sort of capacitor battery and top it up with a solar face

You would need to research it to get the details

It's a very reliable system, I got my second hand ebay one 10 years ago

Edited By Ady1 on 05/04/2018 10:58:32

In an early version of my Electro-Mechanical Fibre optic Clock, I also intended to use solenoids to operate the cylinders. However, I found them to be rather inefficient and abandoned that idea in favour of ratchet wheels and cams to operate the main cylinders. The drive on the final version of my clock is a synchronous motor which has worked very well for a number of years now, and it keeps perfect time. A series of post about it can be found in the clock section, at the top of page 6. It may give you a few ideas. Good luck with your project.

Edited By magpie on 05/04/2018 12:09:51

John and Dave: Thank you for the advice on buck convertors. I shall look into this.

John: have removed two batteries, running it now with six volts. This has reduced the current draw to between 35ma and 75ma. I shall check again at the weekend, though. My everyday multimeter has a small dial and is hard to read at the best of times. It is most useful for estimating than measuring. I have a large AVO tucked away and shall check with that.

Dave: I have a number of LEDs fitted, only one flashing at a time. One is triggered through a transistor, the rest straight from the pins. They all have resistors fitted, but I think only 100 ohm. Perhaps I should be increasing this, at least whilst using LEDs to test the circuits.

Magpie: I had a quick look at your LED clock thread. It looks really impressive and I shall read it in detail. Thank you.

Regards,

James.

Edited By James Alford on 06/04/2018 07:10:50

May be a strange question but is his clock going to display the seconds ? If it is then you could significantly reduce the poewr usage just by eliminating this by using the movement to only show minutes like a digital clock does . I wonder if some form of capacitor discharge circuit to drive the solenoid my be more efficient ?

Edited By James Alford on 06/04/2018 12:35:10