Friday, February 17, 2017

56: Hoop House Temperature Control

A hoop house is the plastic film version of what was once called a greenhouse. These things can be big: 30' by 200', for instance. They can get overheated in the sunshine. I have two granddaughters who have become farmers. Between them they have 4 hoop houses. The daily temperature range inside a hoop house can vary by 70F (e.g., 50F to 120F -- these places are not kind to electronics). Vents with fans are an obvious way to prevent overheating but that spins the electric meter. So the common way to control the temperature is to roll up the plastic film sides. This is generally done with hand cranks. But you have to be on-site to do it. There are also slow-rotating DC electric motors to do the cranking but generally you still still have to be there. I have built and programmed Photon microcontrollers to help keep track of things in a hoop house. This currently includes multiple temperature and humidity sensors, soil moisture sensors plus control of irrigation valves. The user interface is a smartphone oriented web page. For the moment, you can see this at

This saves my granddaughter some concern and some work but the big saving would be to automate the roll-up/roll-down of the hoop sides. So I bought a couple motors from China (the only place they are manufactured, I think). The instructions seemed to be from auto-translated Chinese. Nearly useless, but I mostly figured things out. The nicest feature of the motors is that they have a mechanical limit that protects against over rotating. The idea is that you set (by screwdriver) the physical number of rotations, then apply 24v to the red wire to rotate clockwise or 24v to the green wire for counterclockwise. There is no built-in feedback from the motors. Generally these things are controlled from a power supply that includes a simple 3-position switch:
clockwise / off / counterclockwise.
This power unit also contains an overload fuse: the roller can jam!

My current test setup includes the following:
2 rollup motors (rated 24v DC, 60 watts, about 3 rpm)
1 Power supply (120v AC to 24v DC, 150 watts)
1 4-relay opto-isolated switch
1 ACS714 Hall-effect current sensor (30 amp) spliced-in between the power supply and the switches
1 Temperature sensor
2 Override switches (down button, up button) in case of failure of Internet
UPS (battery backup) with enough juice to roll up or down
1 Particle Photon web-connected microcontroller (i.e., computer) that runs my test software

In small quantities, the motors are very pricy -- esp. shipping and "inspection" (whatever that means).

The ACS714 provides me some feed back from the motors. After extensive (time-consuming) testing, I can detect the following states:

a) motor running
b) motor stopped (the motor's mechanical dial stop setting reached)
c) motor jammed (my program will notice, turn the motor off and send a warning text message)

I still lack "real world" data about jamming since I won't actually install the first system until warmer weather.

Here's what I envision as the smartphone interface for 2 hoop houses/4 motors (subject to change):
password protected, of course

Tuesday, February 14, 2017

55: Use a Photon as an Arduino

"Arduino Mode": Who needs it? Well, I have -- a couple of times. Here are some reasons:

3. A Photon is a 32-bit computer. It is 2x+ faster and has 4x program memory. About the same footprint as an Arduino Nano.

2. Photon analog ports are 12 bits to Arduino's 10 bits = higher resolution readings.

1. Most important: So you can test a Photon setup before Internet has been installed. This is why I've needed Arduino-mode!

I recently had to try a Photon setup "out in the field" and ended up reprogramming it for a Nano. I commented out the Cloud stuff, re-did the analog values, found that I had an "int" overflow (changed it to "long". And had to move the breadboard wires to fit the Nano (and later back for the Photon).

So I complained to Particle and was advised to try MANUAL mode, like this--

SYSTEM_MODE(MANUAL); // this kludge has to be before setup()

void setup() {
    Serial.begin(9600); // you'll need to talk to it
    . . .

void loop() {

    . . .
    if(!Serial.available()) {
        delay(1000); // some number
    // read a command
    ch =; // get 1st character
    if(ch == 'c') { // some value: switch back to connected
        // so you can later flash new code without reset
    . . .

So, for $19 you can have a bigger, better Nano.