I'm trying to create a square wave form from a single AA battery, say 1v. I came across an IC which is essentially a low voltage 555 timer: Semtech SX8122 however it is marked obsolete. I would like to be able to adjust the frequency from 1-10khz. Crystal oscillators seem to be above this range. Are there any other simple circuits or ICs that can operate at this voltage?
With AA you probably mean "Alkaline" battery. These have a full charge voltage of 1.5 V, and not 1 V – and even if you heavily discharged them, most energy is dispersed at voltages between 1.5 V and about 1.15 V (look for "alkaline discharge curve" if you want to know more), so you really don't need to work at 1 V.
The classical NE555 isn't suitable for this kind of battery operation:
- It's a power-wasting nightmare, so batteries are eaten by your oscillator
- more importantly, it can't work at voltages so low.
You can get a CMOS variant of the 555, but you'd have trouble doing much sensible work. If you still want to do that, Spehro's answer is the way to go.
It doesn't solve the current sourcing problems of the TLC551, but it's both cheaper and more versatile if you just used a low-voltage microcontroller. (The TLC551 is of course way less complex, but it's a speciality part, and thus expensive.) The MSP430L092 for example can run at 1MHz with supply voltages upwards of 0.95V.
About your application: you say you want to run an LED string from your poor AA battery – there's a lot of variation, but an AA battery is typically in the 2000 mAh range. So, assuming one LED of your string uses 20 mA, and you want to run a string with 40 LEDs, that's 800 mA of current draw, giving you 2h and a bit in runtime, even assuming 100% voltage conversion efficiency. And that's a conservative guess – many ambient lighting LED strips have higher per-LED draw.
TI has a version of the CMOS 555 (the TLC551) that is characterized down to 1V. It can’t drive much current though, at such a low supply voltage.