Last week, we started selling Moistly, a simple device that helps you remind to water your plants, when it senses that the soil is getting dry. Moistly was designed after quite a few people remarked that they would like a non-connected, simple device that reminds them to water their plants. As I had designed and built GrowGuard, that seemed like a great idea.
This post will explain the process that we went through and how you could do the same, even if you are just a small company or group of friends. We will talk about how the design was converted from Arduino to something better manufacturable, what we did with the enclosure and how we got the part into production.
Idea to Arduino
As I stated, I have quite a bit of experience with Arduino and started with this to do some tests. Using an Arduino and a breadboard, I built a device with a buzzer and LED connected to two Arduino PWM pins. This allows one to generate sounds and drive the LEDs strength with an analog value. In addition, I used the following design to measure the moisture in the soil.
One thing that quickly happened was that the soil sensor started corroding. In order to prevent this, I connected the +3V3 pin of the design to a digital pin instead and only put it HIGH for a 0.1s, when measuring the soil resistance, then putting it LOW again for a couple of minutes: oxidation solved!
After this first success, I drew a simplified schematic and board in Eagle, consisting of:
- ATMEGA328p (same as in UNO)
- 3V coin cell
- Necessary capacitors and 8MHz resonator
- Programming and ISP connections
- Buzzer, LED and (simplified) moisture sensor design
The board design was sent to Itead studio, and two weeks later I had my first real (hand-assembled) Moistly in my hand. Notice that the design has 13 components, not bad given the extensive design I started with.
Now came the issue of battery powering such a device for more than a few days. Fortunately, I already had gotten experience with this. So I used the same techniques and since the ATMEGA was driven directly by a 3V coin cell, there was no issue with power-consuming voltage regulators (LDO).
After a few software tweaks, I was able to measure a sleep current of just 1.8uA and a wake current (which is only for a few 100ms per 5 minutes) to ~2mA; yielding an expected coin cell lifetime of well over two years.
Industrial (=enclosure) design
Around this time, I met the guys of Tweetonig, a industial design firm here in Holland, who have a lot of experience in enclosure and mold design. Together we decided to put the Moistly on the market: I would do electronics and embedded software, they would do enclosure and all visual materials. And so came to be. After sketching and 3d printed test designs, we went for a ‘leaf’ design that would be relevant to the application (plants) and large enough to house all the components (especially a 30mm coin cell and a 8mm high buzzer).
In order to prepare for production, we wanted to make the electrical design still simpler. So what we did was use an ATTINY85 instead of the ATMEGA, remove as many capacitors and resistors as possible, and run the ATTINY of its internal oscillator at 1MHz. Result: Just five components left!
Now that we were satisfied with the PCB and enclosure design, it was time to think about production. As for PCB production, we found a nearby supplier that would be able to do production of PCBs and assemble them at a low cost and at a low startup cost (so no 500-3000 usd that was quoted by some) and with a delivery time of about a month.
As for the enclosure, we decided that a mold would be cost effective if we were to sell at any significant volume. So quotes were requested at a few places and we found a mold maker that was capable, reasonably priced and could deliver in also about a month.
It was a great journey again. It has helped us a lot that both parties already have experience in electronics and enclosure production. We are proud of our first little product together and hope to create many more. With this post, we hope to share some of the knowledge and experiences we have had, and hope to inspire people to do the same.
And finally, if you think that Moistly is useful to you or a friend, then we hope you purchase one in our online store, or share a link on Facebook, Twitter, Reddit or whatever.