OpenSprinkler Extension Board Build Instructions
(Note: all images below are clickable, in order for you to see the full-resolution details.)
Versions
Version 1.3u/v1.4 Extension Board
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The OpenSprinkler extension board uses the same PCB as the main controller, but with only a subset of components. Specifically, these are shift register (74HC595), two 330ohm resistor arrays, eight triacs, one 8-port screw terminal, and two 2×4 pin headers. A 2×4 extension cable is also included. The extension board PCB is marked by a purple label. The soldering instructions are similar to Part 3 of the controller assembly instructions. |
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Solder the components to the PCB. Refer to the picture on the left. |
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Take out the extension cable, plug one end to the main controller’s EXTOUT (right) connector, and the other to the extension board’s EXTIN (left) connector. The cable is symmetric, so it doesn’t matter which end goes to the main controller, as long as you both ends are plugged in the same orientation. In other words, make sure the wire colors are ordered in the same way. The diagram below shows the actual pin connections. If you have multiple extension boards, you can cascade them in the same way: connect the EXTOUT of the previous board to the EXTIN of the next board. |
Version 1.2u Extension Board
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The OpenSprinkler extension board uses the same PCB as the main controller, but with only a subset of components. Specifically, these are shift register (74HC595), 10K resistor, two 330ohm resistor arrays, eight triacs, one 8-port screw terminal, and two 2×3 pin headers. A 2×3 extension cable is also included. The extension board PCB is marked by a purple label. The soldering instructions are similar to Part 3 of the controller assembly instructions. Note: IC socket is not included for the shift register. Please solder the shift register directly to the PCB. |
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Solder the components to the PCB. Refer to the picture on the left. The 10K resistor goes to R1. Most kits should have two 2×3 male headers. Solder one of them to EXTIN (left) connector pinout, and the other to the previous board’s EXTOUT pinout. To cascade multiple extension boards, simply connect the previous board’s EXTOUT to the next board’s EXTIN. Some kits may have two 1×8 male headers. In this case, use a diagonal cutter to cut out two 1×3 male headers, and solder them individually to the pinouts to make a 2×3 pin header. |
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Take out the extension cable, plug one end to the main controller’s EXTOUT (right) connector, and the other to the extension board’s EXTIN (left) connector. The cable is symmetric, so it doesn’t matter which end goes to the main controller, as long as you both ends are plugged in the same way (i.e. the same orientation). Each end is actually a 2×4 connector, with two empty holes. The diagram below shows how the pin connections.
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If you have multiple extension boards, cascade them in the same way. The picture on the left shows an example. The pictures below show two close-up views. 
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Version 1.1 Extension Board
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The OpenSprinkler extension board uses the same PCB as the main controller, but with only a subset of components. Specifically, these are shift register (74HC595), 10K resistor, two 330ohm resistor arrays, eight triacs, one 8-port screw terminal, and two 2×3 pin header. A 2×3 extension cable is also included. The extension board PCB is marked by a purple label, which matches one end of the extension cable. The soldering instructions are similar to Part 3 of OpenSprinkler assembly instructions. Note: IC socket is not included for the shift register. Please solder the shift register directly to the PCB. |
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Insert the components to the PCB and solder them. This is pretty straightforward, except for two notes:
1. The pin headers are 4+2 pins. Insert it such that 4 pins are on the top (DATA, CLK, LAT, QH*), and 2 pins are on the bottom (VCC, GND). Leave the 24V pins open and do not use them. If the pin headers are too long, clip them with a diagonal cutter. 2. Depending on the PCB you’ve received, the 10K resistor may located differently than shown.
This resistor is not crucial, so it’s ok if you leave it out. |
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If your main (master) controller does not already have the 4+2 pin header, solder it now. Again, make sure that you leave the two 24VAC pins open and do not use them. |
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Take out the extension cable. Plug the end with a purple label to the extension board, and the other end to the master controller. The cable has 3+2 wires. Make sure the bottom 2 wires go into the VCC and GND pins.
Basically, the cable should make the following connections (master->extension board): |
Here are two close-up views of the connectors. Note that the wire colors may differ from the cable you received. 
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Hi Ray,
I’m thinking of getting a OpenSprinkler Pi for my home, but would need to have the raspberry pi at the front of the house, and the expansion at the back.
Is it possible to hook up a second 24VAC adapter on the expander board so that the longish cable between the pi and expander doesn’t need to carry the current for the solenoids? I know some ‘missing’ components may need to be added back to the expander board.
Thanks!
The extension cable between the main board and expansion board should be kept short, because the cable carries signal lines. Long expansion cable makes it prone to noise interference. You can try but it may not work well. On the other hand, you can run long wires between the controller / expansion board to the solenoid. If you use relatively thick wires, it can go at least several hundred feet.
I also have the same problem as above.
Current house has 2 sprinkler timers (cheap 20.00 units). One in the back detached garage for the backyard setup and one in the front garage attached to the house for the front yard.
I have a hard time buying 2 open sprinkler units (300.00 plus) to replace both and run two different setups. I wish there was a wireless or even network option to attach a more reasonable price expansion board in the back garage. Running sprinkler wires to the back, under concrete is not worth the cost of an extra unit, but buying two units isn’t worth the cost of switching my working non networked sprinklers controllers out. Any other suggestions?
And say I did buy two units, is there a way to make one a master and one a slave? At min. a software fix for that would be a nice touch. One would be able to control the channels on the slave board.
Sorry for my late response, I didn’t notice this comment previously. Some users have made custom extension cable which allows them to place the expansion board a few hundred feet away form the main controller. However, because the signal transmitted on the extension cable is not encoded, it’s probably not very robust to noise and interference. You can give it a try, but in the end, the time and effort you spent on building a custom extension cable may not be worth the cost.
What about setup instructions for using one as a master and one as a slave? Is it possible for someone who can’t write his own code?
Similar isue as above, with multiple areas that require a longer span between controllers (e.g. 200 ft). Was thinking about using an RS485 converter and a modbus relay board. Is there any such support already built in?