Recently, I have been developing a watch (miniature) version of ClockSquared. One of the main challenges for this device is to achieve good battery life while not making the watch excessively large or hard to use. This can be achieved by taking various power-saving measures that I will discuss in a future post, but what I will discuss today is way to actually verify that the watch’s power consumption is sufficiently low while in use and while in “sleep mode”.
Dave Jones, the author of EEVBlog, developed a great little device that enables the user to measure electrical currents (in ampere), all the way from the pico scale to the base scale. The main advantage of this device is that it does this with very low burden voltage, a concept which is nicely explained by Dave Jones himself here, or by Andreas Spiess here.
The uCurrent Gold is open source hardware and I took advantage of this by porting the PCB documents to KiCad and adding several improvements. Firstly, I added two 0.1 uF decoupling capacitors between the V+ and V- rails and ground (C5, C6) to improve the robustness of the measurement system. Secondly, I added a footprint for a JST-XH connector (J5) which allows the device to be powered by an external battery, e.g. 3xAA batteries. (The higher voltage will also increase the ranges!) Lastly, I added a probe connection point (TP1), which I hope will allow lower-noise measurements (if I ever purchase a scope, that is). I also simplified the silkscreen a bit. Here is a front and back view of the PCB in KiCad’s 3D viewer (some components not shown):
The PCBs were manufactured by PCBWay. PCBWay was very kind to support my work and supply these PCBs to me free of charge in return for an evaluation of the quality of the PCBs. I chose an ENIG finish, red silkscreen and 1.6 mm thick PCB, like the original uCurrent. The PCBs were ordered and were produced quickly. They arrived shortly after, decently packaged in a bubble-wrapped stack:
I ordered ten PCBs but noticed that I had received eleven. I wasn’t planning on assembling ten pieces anyway, but if this were the case, the spare would’ve been helpful in case one PCB had to be scrapped. A nice detail.
The quality of the PCB is very good, in my opinion. The layers are well-aligned and I could detect no functional imperfections. The silkscreen is of good quality and all references can easily be read. I was a bit worried that the pads for the reverse-mount LED (D1) would be too close to the hole, but the manufacturing quality was sufficiently high for this not to be the case (KiCad actually gave me a warning for this). Overall, I am very happy with the service that PCBWay has provided. I noticed that PCBWay offers a larger variety of manufacturing options than e.g. JLCPCB. PCBWay tends to be slightly more expensive, though. Nevertheless, the service that has been provided is excellent and I look forward to assembling these PCBs. I will report on this in a future post.