1volt clock

Hi I have an LCD clock on my window sill. It runs off a 1 volt solar panel from a recycled garden light (by charging a battery so it still works at night).

How can this work at 1v (and other things like 2v PICs) when TTL is ~ 2.5 to 5v? see:

http://www.interfacebus.com/voltage_LV_threshold.html

Thanks

Logic doesn't have to work at TTL voltages. Your mobile phone doesn't, and neither does the processor in your PC.

Thanks,

Yes I think I get that but even the LVCMOS doesn't appear be as low as 1v on that diagram for logic 1.

Do they step up the power supply for 1 volt clocks somehow?

cheers

Yes you could boost the voltage with a switching regulator but then it would draw more current. Or you could just make your electronics work off 1 volt. It's not hard with a custom chip.

Thanks Grumpy_Mike

do you have a link for those chips? I'd like to look in more detail at low volt / low power in general. Most of my electronics revolves around my remote shed and garden where I have no mains power.

I had an idea for a datalogger project that could use a low power solar powered clock to generate pulses to power up an Arduino.

The Arduino does the logging to a shield and then switches off to save power. So the clock pulses, say every, 15 mins, the arduino logs for 20 secs then powers off.

The arduino battery is then only being used for 80 sec in 3600 sec (an hour) which is under 3% of the time, so it should last a long time - months hopefully if it's a 12 Ah solar battery.

Cheers

Custom chips are just that - customised. Unless you're talking of runs of hundreds of thousands, forget it.

There is a reason why conventional logic is at 3V3 or 5V and that is one of noise immunity. When you start running logic lower you need lower noise environments otherwise it is susceptible to interference.
Something like a clock is quite self contained without long wires picking up noise so that is probably why they can get away with it. They also probably leveraged all the development from wrist watches which use low voltages.

As AWOL said a custom chip is one that is made specifically for you, you go to a semiconductor design company and say what you want and they design a chip that does it. This costs many hundred thousands dollars so it is not something an ordinary hobbyist can do.

Don’t confuse low power design with low voltage design they are two different things. Some processors are specifically designed for low power consumption like the MSP430, others like the processor in the Arduino have low power modes but are not as low power.

Yes, sorry that was muddled thinking on my part.

So I can't do very low power with arduino alone. It's tricky though because I am not yet up to making a datalogger out of an XLP chip like those.

I'm confident I can get the datalogging working on arduino, I just need to figure out how to switch it on with a low power "clock" or pulse generator every 15 mins.

The RTC clock on the arduino shield will log the real time, so the pulse generator doesn't even have to be that precise in keeping time. Maybe I could use clockwork XD

But seriously, I think I could use a low-ish power chip (~1 mA) just to produce a pulse every 15 mins and switch the power to the arduino (maybe via a flip-flop) then the last thing the arduino does is switch itself off, until another pulse is applied.

Is there such a chip that doesn't require a lot of programming knowledge, ie is suitable for a relative beginner?

cheers

Is there such a chip that doesn't require a lot of programming knowledge, ie is suitable for a relative beginner?

No The Arduino has a low power mode it is just that it is not the lowest power processor you can get.

I just need to figure out how to switch it on with a low power "clock" or pulse generator every 15 mins.

See:- http://www.arduino.cc/playground/Learning/ArduinoSleepCode

You can use the watchdog to wake the processor every 8 seconds or so (the watchdog oscillator isn't very accurate). You can use this in conjunction with the low power modes to wake the processor decrement a counter, and if the appropriate number of eight seconds haven't elapsed, go back to sleep. When the required time-period has elapsed, you can take your measurements and repeat the cycle. Or use an external RTC with alarm interrupt to wake the processor.

Hello,

Thanks that's all really good stuff. I feel I'm getting a lot closer to my low-ish power device with arduino.

Or use an external RTC with alarm interrupt to wake the processor.

A search of RTC http://pdfserv.maxim-ic.com/en/ds/DS1305.pdf alarm gave two alarms per day for this device (I think, not sure, but the i looked at the datasheet)

I need four per hour. Is there something like this ie four per hour, or better = programmable for period, with low-ish power? I know I am asking a lot with my spec.

(actually I am still looking at my 1v clock - I could run this off a potato, or maybe a lemon. It has a square on the screen which flashes from grey to black each second. Whimsical I know)

cheers

If you don't need too exact of period you can use a 555 timer set to a very long time, its basically what was described lol, have it control a transistor or maybe even right to the arduino since it can supply 200ma if you set it up right you can probably be well within your goal

winner10920 - cheers mate,

what's the RC (time) calc on the 555 for 15 mins? also how do I work out the juice-age. Will it be below 1 mA?

winner10920: If you don't need too exact of period you can use a 555 timer set to a very long time, its basically what was described lol, have it control a transistor or maybe even right to the arduino since it can supply 200ma if you set it up right you can probably be well within your goal

A 555 timer is not truly low power (in the sense of only using a few uA). The problem with Arduino boards is that they have other devices like voltage regulators and USB interface chips that take mA of current all the time even if you put the processor into ultra-low-power mode. A custom board is needed to get proper low-power operation (the ATmega in full sleep mode with watchdog timer enabled is a few uA only, good enough for years from a battery it a very low duty-cycle) Couple this with a DS1307 RTC chip (0.3uA standby) then you can do some interesting things.

Many Thanks to all,

I looked at the datasheet for the DS1307 RTC and it appears to have a programmable square wave output.

I can get one of those in a module I saw from uk sparkfun supplier. I also note there are links to articles on the arduino website.

Cheers

and thanks again

Whilst waiting around for the RTC clock. I tried making a lowish power pulse generator on my simulator. See attached. I guess if I used low power components it would run less than a mW, but most of the ordinary things are in the lab anyway to play with. I’ll try for real next.

Would welcome any feedback.

Cheers