This is a review of an inexpensive MH1230A Chinese bang-bang thermostat that was purchased on eBay for around A$15 complete with thermistor sensor and postage.
Above is the front view of the thermostat. There are many thermostats on the market with similar front panels, but they differ in internals and most importantly, performance and quality.
Above, the rating label is clear and informational, and it does give the sensor parameters. Continue reading Review of inexpensive Chinese thermostat – MH1230A
This article expands on A flexible test panel for microcontroller based power control projects with some enhancements and accessories.
A LED power meter that I had ordered finally arrived (slow boat from China syndrome).
Above, the upper rail contains a RCD, the power meter which displays Volts, Amps, and kW, or pf, hours, and kWh, a DIN mount terminal block for mains, and a 40A SSR on a heatsink. A clip on CT can be used for oscilloscope observation of mains current. Continue reading A flexible test panel for microcontroller based power control projects – #2
A correspondent trying to get his head around old designs was challenged by the Tuned Plate Tuned Grid (TPTG) oscillator in common cathode configuration.
A superficial analysis is that the feedback to the grid from the anode via the anode to grid capacitance (Cag) is in phase with the anode voltage, which because of inversion in the valve means it is negative feed back. How can it cause self oscillation? Continue reading Tuned Plate Tuned Grid oscillator – a simple, but complete explanation
I do a lot of experiments with microcontrollers switching mains powered equipment, and the test beds have always been improvised. It has always been my intention to formalise something for convenience but mainly for better safety.
The article describes a test panel to fill that need.
The panel is constructed on a piece of 3mm aluminium sheet, drilled and tapped to take two sections of 35mm DIN rail for flexible mounting of accessories.
Above is a pic of the test panel in use to test the generic heating / cooling controller (hcctl), a flexible bang-bang controller based on an ATTiny25. Continue reading A flexible test panel for microcontroller based power control projects
Review: magnetic stirrer with heating plate and digital display XB 85-2 documented problems that prevented the device being very useful.
Attempts to tune the supplied PID controller above were frustrated by a lack of meaningful documentation supplied or found in searches on the ‘net, and the fact that the display is sometimes faked to appear that the temperature has stabilised. With any non-zero I term, it behaved badly and some observations suggest that it suffers from integral windup. It is truly a piece of Chinese junk and unusable.
Above is an independent logger capture of the temperature from switch on. There is a large overshoot, and then, no matter what the settings, it oscillates and the lowest amplitude obtained was 1°pp (above). The overshoot is almost as much as observed in manual warm up when power is cut at 40°. Continue reading Fixes #1: magnetic stirrer with heating plate and digital display XB 85-2
I recently had need to attach four wires to a set of pads on a device for programming its microcontroller. The pads for these sort of things are often on difficult to solve pitch, this one is 2mm which is not too bad.
Above is the target and solution.
The target is the four vias right next to the LEDs on the daughter module. Continue reading A little programming adapter for 4 x 2mm pitch pads
This article shows just how easy it is to make an inexpensive low VSWR load for antenna analyser validation / measurements.
Above is an AA-600 sweep of the prototype from 10kHz to 100MHz. VSWR reads 1.02 in ‘All’ mode at 100MHz… better than the inherent accuracy of the instrument.
It is made from two 100Ω 1% 1206 SM resistors purchased on eBay for about $2/100, so about $0.04 for the resistors, and 40mm of bare copper wire (0.5mm phone / data wire in this case).
In use, it is held in contact with the coax socket (in this case an N type) with a pair of disposable plastic first aid tweezers (yep, you can buy them on ebay for about $0.20/pair).
While you are at it, make a good short circuit termination by scrunching up a bit of (clean) kitchen aluminium foil and press that against the coax socket conductors.
Try both of these on your antenna analyser and see how it stacks up.
DL4YHF published a frequency counter design based on the PIC16F628.
The design has been modified by many, copied by even more, and usually without attribution.
This article documents one of these copies (TB-244756 printed under the chip footprint), a $6 kit off eBay which comes with no documentation, though the screen mask is enough to correctly place components.
It turns out to be DL4YHF’s “DISPLAY_VARIANT 2”, the variation is that it uses a common cathode display.
Above the built kit with the 7550 voltage regulator replaced with a 78L05. Continue reading DL4YHF 50MHz counter on a Chinese TB-244746 PCB
I purchased a laboratory style stirrer / hotplate with PID temperature controller for some experiments.
Above, the 85-2 product from Chinese maker XB.
It certainly looks the part and for under $100 looked impressive value… but was it?
Is it safe?
First thing with ANY Chinese appliance is to test the electrical safety. Prior to a full PAT test, I plugged it in on an insulated work space and waved a non-contact voltage detector over the case. Beeeep! The case is hot. Earth continuity (earth pint to case) is zero, there is no connection. This came with an AU plug… so lets look inside at how they wired it up.
The green yellow earth wire is floating look, the end has been tinned so it was or was intended to be soldered to something. The end of one of the screws holding four rubber feet on is more silver coloured than the others, so it appears to have been tacked on to that. Three issues: the screw tension is cushioned by the rubber foot and pressure to case is low so it would not be a reliable low resistance connection; soldered ground connections can melt off in a fault and are unacceptable practice; and the even this had become disconnected and would not have passed a basic electrical test. Chinese Quality!
So with the cover off, it is apparent just a few months after this May 2017 dated build has been put together with rusty steel. Continue reading Review: magnetic stirrer with heating plate and digital display XB 85-2
The generic heating / cooling controller (hcctl) is a flexible bang-bang controller based on an ATTiny25.
The controller will accept 4-20mA input if the input is shunted by a 50Ω 1% resistor (2 x 50Ω 1% resistors is a practical implementation) and the 4-20mA sensor is wired between nominal +24 and the input pin. Note that 4-20mA sensors may operate properly on less than 24V (the one used here is a DIN rail mount that works for 10-24V).
To demonstrate the capability, a Pt100 RTD is connected to a 4-20mA converter and then to a hcctl test module (see above). The test module is driving a small incandescent lamp which is clipped to the RTD to provide a cycling test.
Continue reading 4-20mA Pt100 input for the generic heating / cooling controller