Hi,

As background, I'm in the process of designing a prototype for a new type of antenna - a "software-defined antenna", which will use Arduino as the antenna controller. Arduino will preside over a network of small antenna switches called "J Boxes". Each J-Box is used to switch an antenna segment on or off, thereby quickly retuning a multi-band antenna to resonance for the new frequency.

Arduino must be able to address each J-Box device over a control line, sort of like a LAN, to command that device to open/close it's antenna switch (a SPST relay capable of handling RF switching).

Originally, I chose a "1-Wire" device DS2413 by Maxim, which does exactly what I need; however, upon more careful review, I now see that device's operating range is 0 to +70 C. As these devices will be deployed outdoors in weatherproof housings, they must be capable of operating well in freezing temperatures. The other components I'm using are typically rated for -40 to +140 F. I really like the simple, multi-drop 1-Wire protocol, but these devices won't cut it.

Initial research suggests there are much less expensive microcontrollers and IC's to choose from. The requirements are:

1) Has existing means / protocol to communicate with Arduino (ideally an existing library available)
2) Fast to power up, ready for use (no more than a few milliseconds). Because these devices operate as part of the antenna, they are powered down during transmit and normal operation to protect against RF. These devices must come up ready to go very fast - no "boot" sequence.
3) Up to 256 devices can be addressed on a single multi-drop wire connection, up to 100 meters from the Arduino antenna controller (typically they will be within 10 meters, unless the controller is deployed remotely)
4) Low-power, can operate on 5 to 12 VDC at no more than a few milliamps maximum
5) Moderate switching speed (1 ms. or less) of digital outputs (min. 2 DO)
6) Digital inputs are nice to have, not required
7) The output current drain could be up to 10 to 20 ma. maximum for a few milliseconds during switching (it's controlling a latching relay, so only momentary current is required)
8) Operating temperature from -40 to + 140 F.
9) $2 to $3 each in low volumes

Any suggestions would be greatly appreciated.

Rick

 

I think you could use any small microcontroller, and do the communication via RS-485 or SPI. I looked at the specs for a PIC16F690, and its operating temperature range is -40 to 125C. SPI might be better for your project, because you can put the processor into sleep mode and have SPI wake it up, which the serial port can't do. But the regular power draw is low enough that maybe sleep isn't required.

 

I think you could use any small microcontroller, and do the communication via RS-485 or SPI. I looked at the specs for a PIC16F690, and its operating temperature range is -40 to 125C. SPI might be better for your project, because you can put the processor into sleep mode and have SPI wake it up, which the serial port can't do. But the regular power draw is low enough that maybe sleep isn't required.

That's brilliant, John! Thank you very much for this superb information. Looks like RS-485 can handle up to 256 nodes with the proper terminations, and the PIC16F690 looks great. In fact it may enable me to replace another component currently required to deal with the 1-coil latching relay. The low power sleep mode could certainly come in handy. Best of all, these are available in a variety of form factors.

Thank you!