At IoT – exploration of LoRaWAN – part 2 I reported some quality issues with two low cost SAMD21 Arduino Zero like boards.
In both cases, the bootloader did not work. I did not investigate further but did note that the NVM user row looked like it had been cleared, but just wrote a new bootloader and restored a default user row with protection for the 8192 length bootloader.
Above is one of the culprit boards. Continue reading Arduino SAMD21 bootloader protection
At IoT – exploration of LoRaWAN – part 1 details were given of first steps in a LoRaWAN project.
This article documents some MCU boards used for prototyping solutions.
The Arduino Zero concept was chosen for a modern module supported by the Arduino IDE and with ample memory resources for the LoRaWAN protocol stack and application code and memory requirements.
The boards tested are ‘basic’ Zero boards using the Atmel SAMD21G18 MCU. None of the three boards discussed here had the ‘PRO’ EDBG chip / ‘Programming USB’ port, they had only the ‘Native USB’ port.
Above is the module under test. Continue reading IoT – exploration of LoRaWAN – part 2
This article reviews the Dragino LG02 LoRa ‘gateway’.
Above is a pic of the supplied device, and notably it is supplied without the external WiFi antenna shown in the manufacturer’s literature and seller’s web shop.
Above is a close up of the case with the plastic plug removed from the ANT-3 hole, there is not connector, the device does not have provision to install the external WiFi antenna and presumably has an internal antenna though we might expect that has reduced range. Continue reading Dragino LG02 review
This article documents a project with the Espressif ESP8266.
This project is based on ESP8266 IoT DHT22 temperature and humidity – evolution 3, but uses the Bosch BME280 temperature, humidity and pressure sensor. The BME280 has been around for a couple of years, but recently, modules using the chip have become available on eBay for a couple of dollars.
The objective is a module that will take periodic temperature, humidity atmospheric pressure (barometer) measurements, and in this evolution publish them using a RESTful API.
The example platform used in this article is a Wemos D1Pro. In this case, the D1Pro is configured for an external antenna, and a modification is made to the board to add a 1N34A diode for the deep sleep reset circuit (NodeMCU devkit V1 deep sleep). A right angle header on the top of the board (as seen) and another on the underside on the opposite edge to get GND, +3.3, D3 and D4 for the BME280 sensor. There is less than $25 in parts in the pic above. Continue reading ESP8266 IoT BME280 temperature, humidity and pressure
Several of my IoT projects use WiFi, and its range is quite limited, too short to be practical for some projects.
There are several alternatives, but the emerging LoRaWAN concept looks interesting and is worth a visit. LoRaWAN is capable of up to 20km range under ideal conditions, km range should be reliable in most cases.
The first trial is to adapt an existing project functional requirement to LoRaWAN connectivity.
Above is a block diagram of the working trial. Continue reading IoT – exploration of LoRaWAN – part 1
I bought a cheap Pulsar V233-0060 on eBay, you know, one that was advertised as “was working 10 years ago, just needs a battery”.
Of course if that was true, the seller would fit the battery and describe it as working and get lots more money for it.
Pulsar is one of Seiko’s brands, and this movement appears in Seiko branded watches.
Anyway, as it inevitably the case, it did not work.
External examination revealed that with a good battery, the 32kHz crystal was running, but no motor pulses. A further test with external turbo magnetic drive showed the motion works was working… so now pointing to a coil problem.
Continue reading Pulsar V233-0060 stripped down
I bought a little 4-20mA source on eBay for under $10.
The device has a backlit LCD display, and a rotary encoder with steps of 0.05mA (or 0.3125% of 16mA). The current setting can be set as power on default by pressing the knob. It is supplied with a 250Ω resistor which could be used as a load resistor in projects delivering 500mV FSD.
Continue reading Inexpensive 4-20mA source – review
The 4-20mA loop used for the water sensor needs a source of 24VDC. This is obtained from the battery (3.6-4.3V) using a DC-DC boost converter which runs only when a measurement is made.
This article discusses related issues. Continue reading IoT water tank telemetry project – part 4
It seems that almost all small DC-DC converter modules listed on eBay with LM2577 in the headline actually use the Chinese XL6009 chip which they may or may not state “replaces LM2577”.
But… is it a replacement? Continue reading XL6009 DC-DC converter chip issue
Effect of shorting turns on a tapped air cored solenoid at RF offers a simple model for estimating the effect of shorting turns on inductance (L) and Q.
A correspondent sent me a set of measurements he made of an air cored solenoid using a Q meter.
The coil was a 22t air solenoid of length 99.5mm and radius 31.56mm. Q of the whole coil (L12) was measured at 6MHz to be 475.
L and Q were estimated and measured with three different tapping points at one end of the coil.
Whilst the method described in the reference article does not attempt to estimate the effect of tapping where the unused turns are left open circuit, we might expect than when the unused section is a small part of the coil, that the effect is similar to that if the unused turns were not there.
A model as described in the reference article was constructed.
The notation is L1 is the used part of the coil, L2 is the unused part, L12 is the whole coil with no taps, Lms is measured L unused shorted, Lmo is measured L unused open, like wise for the Q subscripts.
Above, the model results There is quite good reconciliation with the predicted behaviour. Continue reading Effect of shorting turns on a tapped air cored solenoid at RF #2