For an “Introduction to ATtiny” class the ATtiny84 is probably a better choice. The ATtiny84 is essentially a chopped ATmega328.
But, the ATtiny85 is certainly an interesting creature.
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I will probably go with the 85 since I have around ten of them on hand. You bring up a very good point that I should include some information about the tinyAVR family. I started using the 85 not based on a professional review of applicable MCUs but several hobby articles.
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For low power and if you don’t need the extra I/O, I’d use the ATTINY85.
Normally anything I’d use the ATTINY84 for, I just either use the '85 or the '328 instead.
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In the AVR world for low power there is just one choice: can operate at 1.8 V or not. The actual current consumption is almost entirely dependent on the number of peripherals powered and switching. In other words, an ATtiny85 running at 8 MHz / 5 V with no powered peripherals consumes the same power as an ATmega328 running at 8 MHz / 5 V. Enabling timer 0 on both processors raises the power consumption by the same amount.
For low power you need a 1.8 V capable processor (and to run it at that voltage) which is the ATtiny85V (or the ATmega328P).
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I want something that can detect pin change while sleeping and using very little current. When a pin changes, it should wake up and turn on power to a WiFi equipped MCU for a few seconds. I though of using it to turn on a FET to power the other MCU. Can a 1.8V device turn on a FET? Am I thinking correctly of this or is there a better way? The goal would be to get months of running time from a battery supply, I use the Wemos D1 Mini in my classes and like the idea of using it as the WiFi MCU but I’m not tied to it.
If you are looking to detect a state change (not a pulse, but a change), then you could wake the device up every 8s or so using the 128kHz clock, and then when it detected a change have it fire off the 8MHz clock and process the change (send a serial message to the Wifi enabled devices after waking it up with the FET) and then when it’s done, go back to sleep.
The main issue with this is that it’s polling. I believe you can make it service a pin change as an interrupt instead of polling, but it’s been a while since I’ve read that part of the datasheet.
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I want to detect a state change based an interrupt and definitely not use polling. This is a hobby grade project that is not mission critical. I’ve seen articles on this but it had dropped low on the priority list until I saw your PCB project.
Also, the Kicad download is 705MB and is awesomely slow. ~6 hours
Yes.
Examples here…
A Pin Change Interrupt will wake an AVR processor from Power Down Sleep Mode (0.1 μA at 1.8V).
You can also run the processor from the 128 kHz watchdog oscillator instead of the calibrated RC oscillator which dramatically reduces the power consumption.
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That sounds awesome for the front end. When the pin change occurs the goal is to turn a 3.3V ESP8266 for a few seconds. I had planned to use a logic level FET but I think they need near 3 volts to turn on. How can this be done with a 1.8V device. I was an IT type not an EE.
Were I in your shoes I would just use the same 3.3 V supply for the whole enchilada. The difference is about 0.15 µW. As an added bonus the AVR processor in your hand, no matter what it is, will work.
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Big thanks to @malcolmputer and @Brian!!! Its nice to know that we have a couple of professionals that I can reach out to if my project hits a snag.
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I recently designed a 6x3.5" board using EasyEDA and ordered 8(?) of them with a solder stencil for $29 total and had them within a week.
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Thanks for the tip, I’ll add it to the list.
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Just an update for all, @artg_dms has ordered and received the PCBs, and he’s in the process of ordering parts. Depending on the shipping he chooses and how long it takes to get the BOM in a format Mouser likes, we’re probably 3 or 4 days out from having the ability to solder up and test a board.
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Did these ever arrive?
Parts arrived, and I assembled one for test. It looks like the design is good. Art and I are PM’ing back and forth about whether to teach a class on the assembly and usage, or to just meter the parts out for the people who paid for the PCB.
I’ll let him comment further. @artg_dms
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Thanks. No need for further comment. I just wanted to make sure that I didn’t miss the followup. I’ll be on the lookout for next steps.
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I will be updating my Arduino: Exploring the Mighty ATtiny85! class and running it again in early August.
Here’s a link to the previous class with a good description:
https://calendar.dallasmakerspace.org/events/view/5841
Its fun to run the chip on a breadboard but I’m looking forward to pushing one into a socket I just soldered onto a real PCB.
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I was traveling alot the past couple of months. Have I missed anything?
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