Accessing the 4th Axon Uart from behind the USB chip

[madsci1016]

I would like to use the 4th Uart on my Axon for a data logger (the other 3 are being used). Has anyone come up with an easy way to wire to it?

I wish the Axon had jumpers to be able to access the 4th Uart when not using USB.

[SmAsH]

Can you solder well?

[Admin]

What do you mean by '4th Uart'?

USB uses UART1 . . . did you mean that?

I didn't put jumpers on it because, if you use the USB (such as for bootloading) while sending other data to it, you can fry USB.

What are you using the other three UARTs for? If one of them doesn't need a high baud rate, you can easily create a software-based UART on any pin.

WebbotLib works with the Axon, and can do that for you easily.

[madsci1016]

What do you mean by '4th Uart'?

USB uses UART1 . . . did you mean that?

Yes.

I didn't put jumpers on it because, if you use the USB (such as for bootloading) while sending other data to it, you can fry USB.

I don't see how this could be physically possible. If you added a 3x2 header to the Axon, and ran the Uart to one row of 3 and the USB chip to the other; either the USB would be connected via 3 (or 2) jumpers (and making it impossible to connect anything else) or the jumpers would be off and the USB would not be connected.

I will have to look into the soft serial, i just feel kinda silly wasting cycles on a soft serial when the AVR has 4 hardware ones.

[Webbot]

I understand what you are saying: and your suggestion would work.

However: there is always some trade off between physical size and flexibility and complexity for newbs. The additional header would require some extra space (and this board is tight on space) and there is always the problem with removable jumpers that people go and loose them.

Equally you could argue that it would be nice to have additional I2C headers in case you have multiple I2C devices, or additional SPI headers for non-programming SPI devices - or even that each IO pin should have two lots of 3 pin headers - one at Vbatt and the other at +5v (or even a third set with +3.3v). Whilst more flexible the board would be bigger and a lot more expensive (someone has to solder those header pins!).

So the trade off is always cost+size vs how often people need the feature. I would argue that 3 TTL serial outputs is still sufficient for most people/projects.

The other alternative is to look for something like an I2C to UART bridge gadget. Then you could connect lots of them without the processing of a software UART. Yep that adds to YOUR costs - but keeps down the cost for 99% of the user base.

Hope that helps, or at least helps to explain why things are as they are.

[Admin]

Yeap, Webbot is exactly right. There just wasn't enough room for all the stuff that could go on it. I couldn't even break out all the ATmega640 pins!