Improvements for oficial relay shield


Based on my own experience designing a relay shield for the Spark Core (

(I’m basing the following according to the pictures on the website.)

  1. It seems that the shield doesn’t have the unused pins broken out. If that’s the case, I think it will be a great addition. For example, a use case could be:

The user wants to control 3 lamps depending on the ambient light and some internet event, so
he wants to add a photoresistor and connect it to the analog input X.

  1. The shield has a lot of free space, this free space should be for something good, like enabling a prototyping area.

  2. Move the Spark Core to the border, so the USB connector is just on the border. This will:

  • Make the USB connector more accessible. The cable will not hang on the middle of the board.
  • More PCB space is left for prototyping.
  1. The placement of the components could be a little bit optimized in order to release more free PCB space.

  2. I suppose the pictures are from a prototype, but in any case, please put some Silkscreen. On it, please put:

  • Graphic for the components. In particular transistors.
  • Assuming you accept suggestion 1, please put in the silkscreen the name/function of each Spark Core pin.
  1. Mounting holes!!!

That’s it. Kind regards.

1 Like

Thanks for the recommendations @cjenkins !
The latest revision of the relay shield includes most of the improvements you mentioned. The design files are available on GitHub. Tell us what you think of those.


Let me make it easy on you :wink:

I would like to suggest the inclusion of a two way screw terminal for power in parallel with the jack socket be included.

Personally, I prefer mounting holes of 4mm diameter, to take commonly available plastic standoffs, and to make mounting with 3mm screws more forgiving.

Both are good suggestions @nil_orally . The shield does offer solder pads in addition to the barrel jack right now.

I would like to suggest that the polarity of the barrel jack should be shown on the silkscreen.

Thanks @Bootes - would you be willing to make a pull request?

Follow up question to @Bootes, what is the polarity of the barrel connector. Most common is the tip to be positive and the sleeve to be negative, but its really hard to tell from looking at it.

@teatime I believe that’s the case, but @mohit can answer for sure

Assuming the footprint is not botched, the tip is positive:

And assuming reverse polarity protection diode D2 has always been on the board, you can’t mess up if you plug in the opposite polarity :smile:


Yes, I can confirm the innner tip to be positive while the outer shell is GND. This seems to be a widely used standard, but we did put a reverse-polarity protection diode just in case.

Another suggestion for a future revision of the relay shield. Renumber the relays so the pin number matches up with the relay it controls. Currently it is a bit confusing (to a beginner like me) to have D0 = relay 1, D1 = relay 2 etc. Also, I’m not sure if it would be helpful to others but maybe have them start at 2 so D0 and D1 are free for I2C stuff and then pin 2,3,4,5 controls relay 2,3,4,5.

Also, I would like headers mounted for the breakout pins so I don’t need to solder anything to start connecting other devices (as a beginner I’m afraid to accidentally mess anything up soldering).