My fortune cookie last night said I have recently left many things undone, and at this rate I may never get them done. Quite alarming indeed. One of the things I haven’t done well recently is regular posting on this blog. So I’ve decided that before the year ends, I have to remedy this by writing a couple of new posts.

The first order of business today is Raspberry Pi Zero. I am sure many of you have heard of it, which is the latest new comer in the Raspberry Pi family, and it has a jaw-dropping price of $5. Five dollars for a tiny computer that runs a full Linux system, how amazing is that! Well, since announced, it’s in such high demand that it went out of stock at most online stores. I’ve been waiting to get my hands on one for a while. A few days ago I was visiting friends in Long Island, New York and discovered that surprisingly I can get the Zero from Micro Center retail stores. So I went and purchased one in their Westbury store. It took me a while to find it in a locked cabinet, and apparently it’s limited to one board per customer. It’s such an anomaly, because normally things in high demand and so difficult to get would be very pricey, but this is only $5!

The main reason for me to get one is to verify if it works well with OpenSprinkler Pi, as several customers have asked me. The answer is yes, as the video demo below shows. But before you decide to dive in, you should be aware of the hidden costs, which can quickly add up. First, to reduce cost the Zero does not have the 2×20 pin headers pre-soldered, and it doesn’t have a standard size USB connector. This means in order to use it with OpenSprinkler Pi, you need to hand solder the pin headers; and in order to connect it to a USB WiFi dongle, you need a microUSB to USB adapter, which is commonly known as the OTG (USB On-the-Go) adapter. If you are not willing to go through the hassle, you’d be better off staying with Raspberry Pi A+, which is only $20.

Here is a display of three Raspberry Pi’s: version 2 model B, A+, and Zero.

The OTG adapter I ordered hasn’t arrived yet, so I decided to make one myself. It’s quite easy: just cut the connectors from an existing microUSB cable and USB extension cable (which has a USB A female connector), strip them, solder the four internal wires with matching colors, and use some hot glue and electric tape to fix everything in place. I then burned a new microSD card (with the latest Raspbian image) and installed the OpenSprinkler firmware. Plug it into the OpenSprinkler Pi circuit board, and insert 24VAC power supply: Voilà, it boots up in under a minute and I can start turning on and off sprinkler valves right away. There you go, it’s verified! For those who want to see real actions, check out the Youtube video below.

Currently the OpenSprinkler Pi circuit board doesn’t have screw holes that match those on the Zero. The consequence is that the Zero won’t have much physical support other than the 2×20 pin header, which is pretty tight and does provide reasonable support. I will have to modify the board design to incorporate the screw holes. I am half hoping that the Raspberry Pi foundation would release a new version of Zero with the pin headers pre-soldered and a standard size USB connector. Not sure if this will ever happen, but we will see!

NOTE: this is a post that first appeared at the Rayshobby Blog. We are re-posting it here (with a couple of updates) to emphasize that OpenSprinkler is not only made in the USA, but made locally (at the Pioneer Valley region in Massachusetts) to support our local business. Hope you like it!

Since March this year, orders of OpenSprinkler have been increasing rapidly. Within a couple of weeks, we’ve done two batches of OpenSprinkler 2.3 at our local manufacturer — Worthington Assembly Inc. (WAi). Previously I have blogged about OSPi manufactured at WAi, and I’ve shown videos of their SMT surface mount manufacturing pipeline, including pick and place machine and reflow oven. This time, I was able to get two great videos of the selective soldering machine, which is used for through-hole soldering. Check the video here:

One of the main benefits of manufacturing locally is the convenience and excellent turn-around time: every order we placed at WAi has been completed within 2-3 weeks, sometimes within 10 days, which is amazing. Also, if there is any technical issue with an order, we can drop by the factory and get the problem solved right away. You certainly get better pricing with Chinese manufacturers — we’ve done that in the past. But the frequent delay there causes a lot of mental stress, and technical issues often take days to resolve. So over time we’ve learned that the convenience and fast turn-around time with local manufacturer are well worth the added cost.

(Update) We’ve started shipping OpenSprinkler 2.3 since early this year. Compared to the previous version (2.0 to 2.2), the biggest change in 2.3 is that the microcontroller has been upgraded from ATmega644 to ATmega1284, which has twice as much flash memory space, and four time main memory. This provides plenty of flexibility in terms of firmware upgrades in the future. The most recent batch (made in October 2015) also added an AC current sensing circuit, composed of a current sensing resistor and precision rectifier based on op-amp. This allows OpenSprinkler to sense the amount of current flowing through sprinkler solenoids. At normal operating condition, each solenoid draws about 150 to 300mA AC current. Having the current sensing circuit makes it easy to verify how well the solenoids are functioning electrically, and detect early signs of solenoid failure.