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I want to build several IR recieving circuits. At first, I wanted to try and do it without any microcontrollers, but after the discussion here I decided to use an AVR compatible MCU.
I think a MCU from the ATTiny series would suffice, but I want to hear your opinion. Here's a description of the program they'll run:

Basically, the circuits will be used as wireless switches - they will respond to IR commands to control relays. Most of the circuits will only respond to one IR code and control one relay (Although some might control 2-3). I'll use simple IR codes so they won't catch up a lot of memory (For example the circuits will respond to 20 pulses, while each circuit will have a different pulse length, so the reciving code is rather simple).

Other considerations, beside the MCU capabilities:
1. Cost - I'd prefer a cheap MCU, but money is not a real problem.
2. Size - I want the final reciever circuit to be as small as possible, so I'd prefer a 8-pins chip rather than a 16-pins one.
3. Power consumption - The circuits will be installed in a not-so-accessible location, so I want the batteries to last for a long time. And once more, since the circuit should be small, I'd prefer small batteries. A low operating voltage and current is great.
4. Clock speed - I read that by decreasing the operating voltage you can control the clock speed, which in turn also reduces the drawn current. In this case I really don't need those 20MHz those MCUs provide.... I'm pretty sure the program would run fine even on a lower than 1MHz clock speed.

With these requirements, will the ATTiny13A-PU work for me? It seems like the most simple one, with 1Kb program memory and 64 bytes of RAM. Or will I need one with more memory, like the ATTiny85?

By the way, since all these MCUs (Including my Arduino's ATmega328) share the same RISC, will the program size be the same for them all? If so, I could code this program on my Arduino and check the final sketch size, thenI could know what size of program memory I need.

Thanks for your help smiley
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If you're planning to build a standalone circuit (no Arduino board, just the AVR chip and whatever support circuitry you need), cost of the chip is barely a factor.  It's in the $1 to $6 range or so, depending on which IC you use.  I.e., about as much concern as the IR LED's cost. smiley-wink

The ATtiny85 is a good place to start for small AVR projects.  It should have enough pins for you if you just want one IR receiver, and to control a couple relays.  $1.30 at Digikey for qty 1.  That gives you 8K of flash and 512B of RAM, which should be enough for this.  It can also use its own internal 8MHz oscillator, which can be scaled down to 1MHz via the clock divider.

WRT clock speed, whatever you read isn't quite accurate.  Decreasing the power supply voltage does not decrease clock speed, but running at lower voltages usually means you need more conservative clock speeds for stable operation.  I.e., you can run up to 20MHz at 5v, but if you run it at 3.3v, it might not be stable at any higher than 16MHz for e.g.  There's a chart of recommended Vcc vs. clock frequency in the data sheet, but many members here successfully overclock them -- it's luck of the draw.  Atmel only guarantees stable operation per the chart.

Running at higher clock speeds consumes more current though.  So running at lower speeds will save battery life.  You'll also want to use sleep modes, so the clock is not running at all when it doesn't need to.  You then use various interrupts to wake it back up -- things like timer events, input high, input low, input edge detection, that sort of thing.

The IR receiver itself will need to run at all times, so check its current consumption specs for an idea of battery drain.  Relays will be a huge energy suck, so if you can use a latching relay, that helps.  With those, when you trigger it on or off, it stays that way without having to apply constant magnetizing current through the coil.

Finally -- program size.  Compiling for a different MCU will give you an idea, but it's not exact.  For one, it depends on whether your final project will be based on Arduino libraries, or if you use vanilla AVR C/C++.  The Arduino libraries take a lot of space, but they make development easier.  The ATtiny85 isn't natively supported by Arduino, but you can graft that support in with user-contributed libraries.  (I think it's called TinyCore, but I've never used it myself.)

If you do use Arduino libs, they have lots of device-specific includes, so code size will naturally vary somewhat by device.  GCC will optimize the compiled code to include only the functions used by your code, so the fewer library calls you make (and the fewer features supported by the AVR you choose), the less needs to be included in the compiled file.  By using vanilla AVR, you'll be able to shrink your code footprint way down, but at the cost of convenience.  With 8K of flash on the ATtiny85, you probably won't have to worry much about code efficiency.
« Last Edit: September 02, 2013, 08:18:29 pm by SirNickity » Logged

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ATtiny85 decoding "Sony" from cheap universal remote:

http://forum.arduino.cc/index.php?topic=139907.0

There are sending/receiving libraries, but the Dollar Store universal remotes are just too economical, IMO.


Ray
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I'd use a Tiny85 - they're more common (therefore better supported). You can probably find an IR library for it with a couple of minutes googling.

If you want to run off a button battery you'll need a Tiny85V (low power version). Make sure your IR sensor will work at that voltage though.

The biggest power drain will be the IR sensor. You may be able to power it from an I/O pin and power it on/off to save battery.

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If you're planning to build a standalone circuit (no Arduino board, just the AVR chip and whatever support circuitry you need), cost of the chip is barely a factor.  It's in the $1 to $6 range or so, depending on which IC you use.  I.e., about as much concern as the IR LED's cost. smiley-wink

The ATtiny85 is a good place to start for small AVR projects.  It should have enough pins for you if you just want one IR receiver, and to control a couple relays.  $1.30 at Digikey for qty 1.  That gives you 8K of flash and 512B of RAM, which should be enough for this.  It can also use its own internal 8MHz oscillator, which can be scaled down to 1MHz via the clock divider.

WRT clock speed, whatever you read isn't quite accurate.  Decreasing the power supply voltage does not decrease clock speed, but running at lower voltages usually means you need more conservative clock speeds for stable operation.  I.e., you can run up to 20MHz at 5v, but if you run it at 3.3v, it might not be stable at any higher than 16MHz for e.g.  There's a chart of recommended Vcc vs. clock frequency in the data sheet, but many members here successfully overclock them -- it's luck of the draw.  Atmel only guarantees stable operation per the chart.

Running at higher clock speeds consumes more current though.  So running at lower speeds will save battery life.  You'll also want to use sleep modes, so the clock is not running at all when it doesn't need to.  You then use various interrupts to wake it back up -- things like timer events, input high, input low, input edge detection, that sort of thing.

The IR receiver itself will need to run at all times, so check its current consumption specs for an idea of battery drain.  Relays will be a huge energy suck, so if you can use a latching relay, that helps.  With those, when you trigger it on or off, it stays that way without having to apply constant magnetizing current through the coil.

Finally -- program size.  Compiling for a different MCU will give you an idea, but it's not exact.  For one, it depends on whether your final project will be based on Arduino libraries, or if you use vanilla AVR C/C++.  The Arduino libraries take a lot of space, but they make development easier.  The ATtiny85 isn't natively supported by Arduino, but you can graft that support in with user-contributed libraries.  (I think it's called TinyCore, but I've never used it myself.)

If you do use Arduino libs, they have lots of device-specific includes, so code size will naturally vary somewhat by device.  GCC will optimize the compiled code to include only the functions used by your code, so the fewer library calls you make (and the fewer features supported by the AVR you choose), the less needs to be included in the compiled file.  By using vanilla AVR, you'll be able to shrink your code footprint way down, but at the cost of convenience.  With 8K of flash on the ATtiny85, you probably won't have to worry much about code efficiency.

Thanks for your detailed comment, I learned alot. I'll go with the ATTiny85, and I'm sure the available RAM/Program memory would be enough.

ATtiny85 decoding "Sony" from cheap universal remote:

http://forum.arduino.cc/index.php?topic=139907.0

There are sending/receiving libraries, but the Dollar Store universal remotes are just too economical, IMO.

Ray


Thanks. I'm familliar with IR sending/recieving in Arduino, so the program is my last problem here. But I'll remember this link for future reference.

I'd use a Tiny85 - they're more common (therefore better supported). You can probably find an IR library for it with a couple of minutes googling.

If you want to run off a button battery you'll need a Tiny85V (low power version). Make sure your IR sensor will work at that voltage though.

The biggest power drain will be the IR sensor. You may be able to power it from an I/O pin and power it on/off to save battery.


Yes, I decided to go with the 85 version, it looks like the most popular one of the Tiny series, which means there are many tutorials for it online.

So, what's the difference between the 85 to the 85V version? Only the lower minimal operating voltage of the 85V version (Which is 1.8v, comparing to the 2.7v of the 85). What are the current differences? (I don't see any in the datasheet).

My IR recievers have a 2.7v minimal operating voltage, and the current is usually below 1mA. I guess I'll use 2 AA batteries, if they can fit, for a smaller button battery if the AAs won't fit. Or should I use a higher voltage?
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I am really liking the ATtiny85 and it's "big" brother the ATtiny84. Same amount of memory but the '84 chip has 12 I/O channels instead of 6. Both can be easily programmed directly from the Arduino IDE using an UNO as the ISP programmer. So it comes down to how many I/O pins you need.

There is a great Instructable on how to make a "programmer shield" for the ATtiny8x chips...  http://www.instructables.com/id/ATtiny-Programming-Shield-for-Arduino-1/

Based on that Instructable I made my own "development board" that allows me to program and breadboard/test either ATtiny chip using the UNO as an ISP programmer/power source. Quite handy indeed and no need to constantly plug/unplug my IC from the programmer every time I want to test my circuit.
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I was just looking at this yesterday... the "V" version of the chips use less power at the expense of max speed. They top-out at 10MHz.
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