Omatic Labs Zettelkasten

Flux Camper Trailer Power Monitoring

Flux is my power monitoring system on the family camper trailer, its a work in progress and while it's not complete i'm getting useful data from it and it's time to write up the project.

Background

In 2008 I put together a camping power system with 4 x 80Ah batteries, 2 x 120 watt solar panels, 30A Steca solar regulator and a 300 watt inverter. This rig was carted around on many camping trips and provided power for our Waceo fridge (sometimes running as a freezer), loads of lights, charging devices & batteries etc.

In 2011 we bought a cheep (and totally awesome) Chinese camper trailer and the camping power rig had a permanent home, it was while upgrading the system with a DC-DC charger and a 600 watt inverter as well as upgrading the power distribution and boxing the whole kit up I came up with the plans for a power monitoring system.

Overview

All the sensors in the system hook up to a Freetronics Ether Ten Arduino compatible ethernet enabled board.

The Arduino samples the sensors as fast a possible in a tight loop then every second publishes the average for that second via MQTT

The MQTT broker is Mosquitto running on a Raspberry Pi that is also part of the monitoring rig.

Python scripts process the raw sensor data and republish to MQTT and log to Graphite running on the Raspberry pi. Python scripts are run by Supervisor

The rest of this post will detail the sensor components and another article will cover the MQTT and Graphite components.

_graphs

Sensors

Voltage

Voltage is sensed via a simple resistor divider. Voltage is divided by three so the Arduino can safely monitor voltages up to 15 volts.

Current

There are 9 current sensors in the system. The main current sensors are 2x 50A Allegro ACS758 sensors. One is between the batteries and the solar regulator the other is between the batteries and two two devices that don’t go though the regulator a 30A DC-DC charger (for charging from the alternator) and a 600 Watt Inverter.

At the time I put the rig together there only one ACS758 breakout I could find was one by flytron.com i'd like to upgrade to this one on Tinde as its easier to hook up to high current cable.

The rest of the current sensors use the Allegro ACS715, I'm using breakouts from Pololu in this case.

The load from the regulator gets fused and distributed by a Blue Sea ST Blade Fuse Block from the 12 volt shop and i've got a current sensor on each channel and an extra on solar input.

All of the the Allegro ACS715 are hooked up to the Freetronics Ether Ten though a multiplexor. I'm using the Sparkfun CD74HC4067 Breakout

0 Geek
1 Inverter
2 Pump
3 Fridge
4 Freezer
5 12 Volt Aux
6 Solar In

Temperature

Temperature sensors are still on the to do list but will be at least 3 x Dallas Semiconductor ds18b20 onewire temperature sensor. I've used them extensively in the past and they work pretty well.

RTC

The Arduino also has a DS1307 Real Time Clock this dates from an earlier design that had the Arduino logging data to SD card. It's still useful for the Arduino to have the time. One current hole in the system is the Raspberry Pi needs a RTC or a GPS as well.

Networking

There is a 5 port 10/100 switch in the rig for networking. Its a D-Link DES-1005A. It's nice and low powerd running at a maximum of 0.9 of a watt.

I've also got a TP-Link TL-MR3020 travel router that can optionally be hooked up for when I need wifi or internet connection.

Monitoring & Networking Power

So the EtherTen is powered by 12 volt from the regulator/batteries and using it's onboard regulator. It needs a bit more that five volt as it as and it makes it easy to hook up the voltage divider for sencing this way.

All the other devices: the Raspbery Pi, The 5 port switch and the optional travel router need 5 volt power. 12 volt to 5 volt regulation is taken care of by a Pololu Step-Down Voltage Regulator D15V35F5S3. It's a bit overkill but I didn't want a smaller regulator working flat out all the time and the raspberry pi can be fairly finkky about clean power. The Pololu regulator works great.

Reliable MQTT connections

So try this, go and restart your local MQTT broker. I'll wait

So how did that go?

If you like me based your MQTT clients code on the example code then you probably have some hung clients than need resetting.

So the Arduino/C examples has this code..

void loop()
{
    client.loop();
}

And the python examples have this..

while 1:
    client.loop()

Both simple to understand for starting out but if anything happens to you broker or there is a network problem etc your client is borked.

It fairly easy to fix though, we just don't assume we have a connection when we call client.loop and if we don't have a connection then lets connect.

Arduino/C

  if (client.connected ()){
     client.loop();
  }
  else {
    Serial.println("MQTT Broker Connection Down");
    if (client.connect("Shed_Temp","shed/will",0,0,"Shed Temp Fail")) {
       client.publish("Status","ShedTemp ReStart");
       Serial.println("MQTT Broker Connection Restated");
    }
    else {
      // Don't flood the broker with connections and it's already down so we don't need to worry about a delay disconnecting the client
      delay(15*1000);
      Serial.println("MQTT Connection Delay");
    }
  }

Python

def connectToBroker():
    client.will_set('jarvis/will/local', payload="Jarvis Local Fail", qos=0)
    try:
        if not client.connect("127.0.0.1"):
            client.subscribe("temperature/#", 0)
    except socket.error, (value,message):
        print "Could not open socket: " + message
        time.sleep(5)

while 1:
    try:
        if client.loop():
            print("Broker Connection Error")
            connectToBroker()
    except socket.error, (value,message):
        print "Could not open socket: " + message

While updating my clients code I've also taken the opportunity to setup last will and testament so i get a MQTT message when the clients disconnect. I intend to hook this up to MQTT Warn so I get notifications when MQTT clients disconnect unexpectedly.

What I learnt about reflow this week

So my second go with my reflow oven was a bit of a fail. So time for some more learning from the internet and testing.

Things I now know.

The T962 oven uses infrared heating element, thus black IC’s heat up faster than other components and white things like the WS2812’s I was trying to reflow will reflect heat and need a bit of a longer time to reflow properly.
I rate SparkFun Rejuvenating Solder Paste with Tim Holmberg
Adafruit also has a great series of pages on SMT Manufacture
Adafruit recommend these SMT Stencil Wipes but so far baby wipes seem like a fairly good alternative.
The sparkfun Solder Paste Stenciling tutorial is well written, funny and made me think a bit more about the saftey aspect. Wear gloves and read the material safety data sheet’s

I've been getting great results cutting my own stencils, I'll save the details for another post soon.

Reflow Oven

So I’m making that big move from building circuits with mainly though hole parts and breakout boards to working with surface mount parts.

I’ve read a lot of articles on surface mount prototyping and I have a lot of respect for the hand soldering ninjas that can work with crazy small SMD parts. But I've built up a bit of an opinion about working with surface mount technology.

Surface mount technology is designed to be assembled using pick ‘n place machines and soldered using reflow ovens. So the best way to prototype with surface mount parts is to make a workflow as close to the manufacturing process as possible. After all its what the parts have been designed for.

I’ve always felt that the key thing in any job is having the right tools. Sure you can do jobs with other tools but it’s always more effort, usually frustrating and often a poorer result.

So the pick and place thing I’ll talk about in a while this update is about reflow ovens.

Alt text

So I went for the cheep Chinese T-962 reflow oven. I’ve read good and bad things about the units, seems mostly luck of the draw. One thing I did do before running it the first time was to rip it apart and replace the masking tape with Kapton tape following the advice from this instructable.

Alt text

Now it looks much better more “Apollo Space mission” than before.

I’m aware of other hacks on these ovens and controller upgrades that cost as much as the ovens. I’m not planning on any further changes other than some kind of fume extraction unless I have problems with reflowing larger boards.

links