Choosing Components for a Design

Although it has been a while, my most recent post about the design of the Wireless Sensor Module discussed the power subsection. Today I’m going to briefly talk about the choices for some of the other components.


I knew I wanted to include the USB interface on the sensor module for several reasons:

Stenciling and First Bake

I’ve been a bit busy for the past few weeks in the professional sphere, developing firmware, evaluating hardware, and seeking out new projects. As a result, I have quite the backlog of topics I want to discuss. Today I’m going to follow up on the previous post about building a reflow oven, showing the first bake and results.

I had a remaining bare PCB from the Wireless RH/Temp Sensor Module project I’ve been working on, which turned out to be an excellent test for the oven. Knowing I would … Continue reading

Inside a MicroSD Card

I’ve been working with the BeagleBone Black and discovered today that I had a bad SD card. Not only could I not access it, but it was also getting hot. Instead of just throwing it away, I decided to do what any other curious person would do – I removed the solder mask so I could get a look at the layout.

These devices are basically just PCBs with flash memory molded into the substrate. I do a lot of PCB layouts, but this was particularly impressive to me, given the trace/space distance … Continue reading

Hub Shields Arrived!

I’m getting a bit ahead of the posts here, but I just received the bare boards for the other end of the Wireless RH/Temp Sensor system.

On the other end of this system, there needs to be a device to collect the data being generated by the sensor modules. I chose to go with a daughter board to the BeagleBone Black, which already includes an Ethernet interface to push the data to a server. The shield (cape, etc.) contains the radio device for receiving the data, the standard cape EEPROM, another RH/Temp … Continue reading

Building a Low-Cost Reflow Oven

Whenever I have a project that I’m working on that involves custom hardware, personal or professional, I have typically assembled PCBs by hand. It takes time, and can be tedious. In low volumes (<5 pcs.) it isn’t too bad. I could send them out to have them populated but this can get expensive, especially for low volumes. If you research reflow ovens or hot air baths, they can be quite costly and I couldn’t justify purchasing one without doing it all the time. But, there are other options.

I had heard about people converting toaster ovens into cheap … Continue reading

Seriously, Arduino?

I’m in the process of converting a toaster oven into a reflow oven, and I opted to use the Arduino Uno + Rocket Scream Reflow Oven Controller Shield as the PID controller.

So I’ve disassembled the oven and went to mount the Uno on the outside using the four mounting holes which are meant for 4-40 screws. I noticed that when I installed the standoffs on the enclosure of the oven that one of the standoffs would likely short to the AREF connector underside pins.

What’s worse however, is that on the same hole, the head of a standard 4-40 … Continue reading

Power Requirements

Now that the critical elements of the Wireless RH/Temp Sensor Module have been chosen, it’s time to determine the power architecture.

We’ve chosen the devices such that both the STM32 microcontroller and the TI CC1175 transmitter will be powered by the same voltage – 2.5V. One thing I’ve learned in doing mixed-signal designs is that you generally don’t want to share a voltage rail between the analog and digital submodules. The rationale is that in the digital domain IO lines are switching constantly, causing transient current requirements at the regulator. If your PCB is poorly laid out (interruption in the … Continue reading

Which Brain to Use?

With the widespread availability of devices today, you would be hard-pressed to find a microcontroller that didn’t meet the needs of simple hardware designs. A system such as this could easily be driven by an 8-bit core, like the ever popular Atmel AVR series devices, which are now driving millions of Arduinos worldwide.

As a side note, my embedded hardware design background began in the early 2000’s, using Motorola (now Freescale) 68HC11 devices. For anyone that doesn’t remember this series, it was extremely popular in the 80’s and early 90’s. The particular variant I … Continue reading

Choosing a Sensor

I’m back to discuss my choice of sensor for the Wireless RH/Temp Sensor Module. I wanted to capture a few simple requirements with the device.

  • Should be PCB mount, preferably SMT.
  • Should be capable of automated assembly, to avoid hand-placement in production.
  • Have an accuracy of ±3% RH or better.
  • Have an accuracy of ±0.5°C or better.
  • Have a resolution of 10-bits or better.
  • Have a response time of 10s. or better.
  • Needs to operate at the VCC rail of the device.

With regards to the system VCC I chose 2.5V to allow it to operate in the bottom-end of … Continue reading

Intro to the Wireless RH/Temp Sensor Module

For a while now, I’ve wanted to have the capability to monitor isolated environments for changes in relative humidity and temperature over time. There are certain areas of our house that always seem hotter or more humid, especially in the summer. I’d like to have measurement nodes to confirm this by logging it over time, which will allow my to take some corrective action in the worst areas.

So the major requirements become: