VU3SQM offers an interesting directional coupler based on a Sontheimer coupler, and using AD8307 power sensing for a nominally HF coupler. I must say that I am not a fan of Sontheimer couplers… but that is what the board uses.
This article lays out a preliminary design review to assist in selection of appropriate toroids, and ordering of the needed parts.
Above, the top side of a PCB. Continue reading VU3SQM directional wattmeter build – #1
I have an inexpensive (~$10 inc post) digital temperature controller that was observed to have very high RF emissions and was unusable because it was incompatible with radio operations here.
There has been enhanced firmware for a STC1000 controller based on a PIC chip, but in my experience, most seem to be made with an STM8S003F3 chip. More recently, what appears to be a port of the PIC software to STM8 has been published at https://github.com/Emile666/stc1000_stm8.
The enhanced firmware is directed at home brewing for control of long running fermentation processes etc, incorporating storage for a number of multi-step programs (profiles). It is not really suited to more general applications like a fridge controller as for example it is more difficult for the common operation to set the set point.
I thought it might be entertaining to try it out.
Installation of the firmware was straight forward, I had the necessary programming adapter and software.
Interestingly, after updating the firmware, the device would not start on its original power supply. My suspicion is that the new firmware runs the LED display at higher duty cycle and the power supply could not withstand the load.
Since the power supply had RF emission problems, it was removed and the device converted to 12V DC.
Above, the large components of the switched mode power supply were removed, a Polyswitch protective device installed and input routed to the output terminals of the old 12V output switched mode power supply (white wire is -ve, brown wire is +ve). Continue reading STC1000 firmware change
On Thevenin’s theorem looked at a simple source network to demonstrate some key characteristics and limitations of Thevenin’s equivalent circuit.
The example network used was linear in V,I for all V,I combinations possible. Let’s now look at a network that is not linear for all V,I, but is sufficiently linear over a sub range to be usefully modelled using Thevenin’s equivalent circuit.
For the purpose of discussion, we have a Black Box with just two terminals and is a source of DC voltage and current, and the internal implementation is hidden from us.
A series of measurements is made with different load resistors attached and the voltage and current at the terminals is recorded and plotted uniformly stepped currents.
The V,I characteristic is clearly non-linear, but on closer examination there are two fairly linear regions, from 0.008 to 0.060A and 0.08A to 0.1A. It is a device that is usually used in the region below the knee, and for our application, let us concentrate on 0.008 to 0.030A. Continue reading On Thevenin’s theorem – #2
Seeing another long running discussion on QRZ about transmitters and antennas, and maximum power transfer and Thevenin equivalent circuits prompts some discussion.
Thevenin published his theorem in 1883, the following is an English translation: Continue reading On Thevenin’s theorem
I have started using Arduino Pro Micros recently, and sourced inexpensive clones from China.
Experience is that all manner of inexpensive small microcontroller modules from China are likely to have issues with the bootloader: it isn’t there, it is back level, not suited to the actual clock speed.
I have come to routinely install a current / known / working bootloader to avoid wasting time down the track.
The Pro Micro does not have an ISP header, and the QFN package does not suit a chip adapter, so the next option is an adapter that can connect to the board with no pins, male or female headers, top or bottom.
Above is an adapter built on a small piece of Veroboard. If you are ging to copy it, make it one row of holes higher. I did initially, and in a miscount of rows, I incorrectly removed the top row. The black mark identifies the pin 1 of the Pro Micro, and the adapter connects to the side with the /RST pin.
The headers on the adapter engage JP6, preserving the pin ordering, pin 1 to the black mark on the veroboard.
Continue reading ISP adapter for Arduino Pro Mini / Pro Micro
This series documents a set of experiments to explore LoRa for a telemetry application. Note this is simple multipoint to point LoRa, it does not use LoRaWAN.
IoT – exploration of LoRa – part 1 outlined a simple direct RESTful submission to Thingspeak from the LoRa – Wifi gateway.
IoT – exploration of LoRa – part 2 outlined a simple RESTful submission to Node-Red from the LoRa – Wifi gateway.
This article describes a direct MQTT submission from the gateway. In this case the gateway converts the binary LoRa payload into more friendly MQTT key,value pairs.
The block diagram above shows the information flow between the main elements. Continue reading IoT – exploration of LoRa – part 3
This series documents a set of experiments to explore LoRa for a telemetry application. Note this is simple multipoint to point LoRa, it does not use LoRaWAN.
IoT – exploration of LoRa – part 1 outlined a simple direct RESTful submission to Thingspeak from the LoRa – Wifi gateway.
This article introduces an intermediate flexible and extensible Node-Red flow.
The block diagram above shows the information flow between the main elements. Continue reading IoT – exploration of LoRa – part 2
This series documents a set of experiments to explore LoRa for a telemetry application. Note this is simple multipoint to point LoRa, it does not use LoRaWAN.
The block diagram above shows the information flow between the main elements. Continue reading IoT – exploration of LoRa – part 1
T962 IR reflow oven rework documented rework of the inexpensive T962 IR rework oven. This article reports some tests on various modules.
The solder cream used is cheap Chinese 63/37 tin/lead solder cream that has been in the fridge for a couple of years, so it is past its use by date.
Solder cream was applied to pads using a pneumatic drive of a 10ml syringe with #22 blunt needle.
A U shaped piece of 0.5mm copper wire was placed on the oven drawer tray and the boards placed on the wire. This to isolate the boards from the thermal mass of the drawer tray.
The program used is shown above. Continue reading T962 IR reflow oven rework #2
This article documents the rework of an inexpensive Chinese IR Reflow Oven for PCB assembly.
The product is widely sold and quite modest price, but is properly criticised for a number for problems that are easily fixed in the hands of a competent person. Continue reading T962 IR reflow oven rework