Description
I recently designed a system using the Pro Mini 3 and the Pro Mini 5 modules. The mini3 interfaces with the Sparkfun FS-3000 air flow sensor. I've had no issues with this pair. I've attached a block diagram for reference. Also part of this design is a Pro mini 5 module. This module reads the speed data from the Pro mini 3 and holds it until the I2C master requests it from the Mini 5. The master device is a Spektrum AR637T radio receiver used in electric RC planes. The AR637T receiver sends the speed data to the ground transmitter through the telemetry channel. Everything worked but there was one concern I had. When I programmed the Mini 5 with the Arduino IDE. under the tools menu, I expected I'd have to select the Arduino Pro Mini option with the 5V/Mege 328P version selected. However I could not download to the module after compiling. I tried the selection of Arduino Uno Mini and this worked, i.e. I was able to download and the module worked fine in the system.
I accepted this since everything was working, but it was a concern because it wasn't what I expected.
However, I ordered 3 more Mini 5s to build up more systems and these new units would NOT allow downloads unless the Arduino Pro Mini was selected along with th5 5v Mega 328P option. Everything compiled and downloaded fine. This is what I expected. But, none of the the modules would not link up with the master over the I2C bus. I dug a little deeper and observed that it takes over 400ms for the Mini 5 code to start executing after power up reset which makes it too late to respond to the initial polling by the bus master. The radio master initial poll for I2C devices comes after 250 ms from power up and if a slave doesn't respond to this first poll, it is not polled again. I tested this by making sure the Mini5 had power before the radio did and it linked up just fine. But in the final design the Radio master, and my Mini 3 and Mini5 all power up together. I used the Sparkfun FTD module connected to a USB port to download. One for the Mini 3 and another one for the Mini5.
I then saw a post about this and someone suggested to use the ISP method for programming which I set up. Everything downloaded and there was only about a 50 ms delay and the Mini 5 linked up and worked fine.
So my questions are:
- Why did the first 2 Mini5 modules not have the 400ms delay out of the box. And I used the USB cable for programming.
- Why did the first 2 Mini 5 modules need the Arduino Uno Mini as the board selection and not the Arduino Pro Mini option.
- Why did the subsequent 3 Mini 5 modules have a significant start up delay out of the box.
- What is different between these two orders of Mini 5s?
Thank you for helping me with these questions.
Steve
True Air Speed Sensor for Stall Warning Block Diagram.pdf