How to make a PCB based on ATtiny easily updatable by end users?

Question

I've made a prototype PCB containing an ATTINY 4313:

Each time I want to change the program, I upload it with an Arduino used with the "Arduino as ISP" sketch.

If one day I sell such a module to consumers, obviously I cannot ask them "please use an Arduino as ISP to update the new version of the firmware".

Which components should I add to a simple ATtiny to make the firmware updatable via a USB cable for end-customers?

The ideal UX for customers would be:

• people download the new firmware
• they connect the PCB to computer via USB
• if possible with no software to install on their computer, they can update the firmware (maybe by just dropping a file on an USB appearing as a disk / flash drive?)

Answer 1

To program the Attiny via USB, you'll need an external programmer, as you've noted: something like your arduino.

Going that route makes no sense, because your programmer would be more capable than your target microcontroller, so you'd drop the ATTiny alltogether.

Instead, I'd recommend simply abandoning the ATTiny and go for one of the many microcontrollers that actually come with USB built in. Some even come with a USB bootloader, where upon power up, for a short duration, the MCU (without any help of you!) opens a virtual serial port where you can just write your new firmware to.

If you want the comfort you describe (dropping files), you'd use

• a microntroller that has USB built in
• a modern microcontroller RTOS that emulates a mass storage device where you can just drop a firmware file and reboot to use the new firmware.

I think mbed is an RTOS that offers that, and it for example runs on the inexpensive LPC series of NXP microcontrollers (and many, many, many other ARM MCUs).

So, what you want exists, but it's really not going to be based on the ATTiny4313 – by the way, a generally strange choice in platform, because you get the "resource poverty" of the ATTiny family for the price of a fully-fledged 32 bit ARM processor that would integrate USB.

Answer 2

Take a look a the micronucleus bootloader...

https://github.com/micronucleus/micronucleus

It allows an ATTINY to accept a code download over a (slightly hackey) USB connection. It is widely used and well supported.

Here is an example of the hardware that uses only a handful of passives to add a minimal USB connection to an ATTINY...

From the excellent Digispark, one of the thousands of boards that use this technique.

Note that this does require some software on the host PC to download the code, but you can use either the Arduino IDE or the AVRDUDE utility - both of which are widely supported on all major platforms.

Answer 3

The simplest way to do this is to replace the ATtiny with a slightly better processor, which has USB support. You'll then need to program it to allow USB upload. I could just reccomend you a processor, but instead, I'll walk you through the process I would go through to pick one.

1. It sounds like you've been working on the ATtiny and arduinos. These are both AVR 8-bit processors. So I'll assume you're familiar with the AVR world and I'll look for another AVR. Though you'd get a lot more bang for your buck looking at an ARM processor.

2. AVRs were made by Atmel, who were bought by Microchip. So I go to the Microchip parametric search page and click the "all products button".

3. Then I look for what (I assume) you want. Under "CPU type", I choose "8-bit AVR MCU", and under "number of USB modules" I pick 1. I click the "5k pricing" column to get them listed from cheapest to most expensive.

Top of the list is an ATmega8U2. If you have any other requirements I missed, you can change the selections and see what you get. For example, if the 20MHz clock is important, you can select that, and then the top option will be a ATxmega16C4.

The USB-equiped ATmegas work with Atmel's DFU bootloader and Atmel FLIP. It's not quite as simple as drag and drop - the customer would need to run a little program - but it is quick and easy to set up.