Here’s a useful tool for the kit, a digital angle gauge/protractor. These use a silicon sensor to show the number of degrees the unit is out of level.
Magnets!
Magnets are provided in the base, so the tool can attach to any ferrous surface.
Battery Box
Power is provided by a single AAA cell.
Main PCB
Removing the rear cover reveals the brains of the unit, and there’s not much to it at all. The main microcontroller is a CoB-type device, so no part numbers available from that one.
Sensing Element
The IC to the left of the main microcontroller is the sensing element. There’s no markings on this inclinometer IC so I’m not sure of the specs, but it will be a 3D-MEMS device of some sort.
Power Supply
The other side of the PCB has the power supply for the logic, and a serial EEPROM, probably storing calibration data.
For a long time I’ve needed a decent vacuum desoldering tool, as I do much stripping of old PCBs for random parts.
Solder wick works well for most things, but it’s expensive & can be fiddly. It also doesn’t keep very long as the copper braid oxidises & after that point it never seems to work particularly well, even when soaked in fresh flux.
Desoldering Station
As usual eBay to the rescue! I managed to pick this one up for £80.
Vacuum Pump
Removing the lid reveals the internals. Front & centre is the vacuum pump, with the mains supply behind it. There’s also a very noisy cooling fan at the back. Not sure why since the unit never gets warm enough to actually warrant a fan.
PSU
On the other side is the PSU. This is an 18v 12A rated SMPS, with a bit of custom electronics for controlling the iron element. Mounted to the back case is a small black box, more to come on this bit.
PSU Board
Cracking the case of the PSU reveals a pretty bog-standard SMPS, with a surprising amount of mains filtering for a Chinese supply. The DC outputs are on the right.
From the rail markings, this is clearly designed to output some more voltage rails – possibly for other models of unit. In this case though, a single 18v rail is present. The iron’s element connects directly to the supply, controlled via an opto-isolated MOSFET.
Chinese Voltage Regulation
As both the fan & the vacuum pump motor are 12v devices, some provision had to be made to reduce the 18v from the power supply to a more reasonable value. Inside the black plastic box are a pair of 1Ω 5W power resistors, connected in series. The output from this connects to the fan & vacuum pump. Because cheap, obviously.
Controller
Finally, here’s the controller PCB, the main MCU is an 8081 derivative, with a Holtek HT1621B LCD controller for the front panel temperature readout. Iron temperature is achieved by a thermocouple embedded in the heater, I imagine the potentiometer on the left side of the PCB is for calibration.
Finally, after a couple of weeks wait time, the fan controllers for the power supplies have arrived. They’re small boards, which is good for the small space left inside the case of the supply.
Controller Boards
Here they are. I’m not certain what the pair of potentiometers are for – there’s no mention of them in the documentation. Possibly for calibration.
Beepers are supplied so an alarm can be heard if the fan fails – very useful for this application.
Controller Closeup
Here’s a closeup of the PCB. Options are set with the DIP switch bank on the left, details for that below. The main IC is a STM8S103F3 flash microcontroller.
Temperature Probe
The only issue at the moment is that the temperature probe leads are much too short. I’ll have to make a small modification to get enough length here.
Here’s all the details on the boards, more for future reference when they undoubtedly vanish from eBay 😉
Specifications
Working voltage:DC12V
Circuit load capacity: maximum current per output 5A, the bus currents up 9A
Output Range: The first channel 20% -100%, or 40% -100% (TFL = ON)
The second channel and the third channel 10% -100%
(Note: Above range only for PWM range, the actual control effect will vary depending on the fan.)
Temperature probe parameters: 50K B = 3950
Thermostat temperature zone error: error depending on the temperature probe, generally 3-5%
Stall alarm minimum speed: 700-800 rpm
Function setting switch Description:
TFL (No. 1): The lowest temperature channel PWM setting, when ON state FAN1 PWM minimum is 40%, when OFF the minimum PWM of FAN1 is 20%.
TP1 TP2 (No. 2,3): Temperature channel control temperature zones are interpreted as follows (need to used with the temperature probe):
TP1
TP2
Accelerating temperature
Full speed temperature
OFF
OFF
35℃
45℃
ON
OFF
40℃
55℃
OFF
ON
50℃
70℃
ON
ON
60℃
90℃
When the temperature lower than the accelerated temperature, then output at the minimum rotation speed; when it exceed over the full temperature, then always output at full speed.
BF1 BF2 (No. 4,5): corresponds FAN1 FAN2 stall alarm function switch, when the corresponding open channel fan break down, the controller will alarm with soundand light (works with buzzle), alarm will automatically eliminated when the fan is rotated recovery . If BF1 and BF2 both are open (ON), the FAN1, FAN2 have any one or both stops, the controller will alarm!
Now the final bits have arrived for the SWR Meter module, I can do the final assembly.
SMA Connectors
Here the SMA connectors are installed on the side of the eBay meter, for forward & reverse power tap.
These are simply tee’d off the wiring inside the meter where it connects to the switch.
Uncalibrated
The meter is connected to the module via a pair of RG58 SMA leads, above is a readout before calibration, using one of my Baofeng UV-5Rs.
I’m using my GY561 eBay Power Meter as a calibration source, and as this isn’t perfect, the readings will be slightly off. If I can get my hands on an accurate power meter & dummy load I can always recalibrate.
Tools are only as accurate as the standard they were calibrated from!
After calibration, here’s the readings on 2m & 70cm. These readings coincide nicely with the readings the GY561 produce, to within a couple tenths of a watt. SWR is more than 1:1 as the dummy load in the GY561 isn’t exactly 50Ω.
High Power VHFLow Power VHFHigh Power UHFLow Power UHF
Shortly I’ll calibrate against 6m & 10m so I can use it on every band I have access to 🙂
The latest addition to my radio shack is the GY561 frequency & power meter, which has already come in useful for measuring the output power of all my radios.
GY561
It’s a small device, roughly the same size & weight as a stock UV-5R. Power is provided by 3 AAA cells.
Display
The display is a standard HD44780 8×2 module. The display on this unit isn’t backlit, so no operating in the dark.
Cover Removed
The cover pops off easily to allow access to the internals, without having to remove any screws!
The 4 screws on the back of the unit hold the heatsink plate for the 50W 50Ω dummy load resistor.
Removing the cover reveals a couple of adjustments, for frequency & RF power calibration.
There are also 3 tactile switches that aren’t on the front panel. According to the manual (which in itself is a masterpiece of Chinglish), they are used to software calibrate the unit if an accurate RF power source is available. I will attempt to do a reasonable translation when time allows.
Disassembly further than this involves some desoldering in awkward places, so a search of the internet revealed an image of the rest of the internal components. In the case of my meter, all the part numbers have been scrubbed off the ICs in an attempt to hide their purpose. While it’s possible to cross-reference IC databooks & find the part numbers manually, this process is a time consuming one. Luckily the image I managed to locate doesn’t have the numbers scrubbed.
Total Disassembly
Under the LCD is some 74HC series logic, and a prescaler IC as seen in the previous frequency counter post. However in this unit the prescaler is a MB506 microwave band version to handle the higher frequencies specified.
In this case however the main microcontroller is an ATMEGA8L.
This is complemented by a SN54HC393 4-bit binary counter for the frequency side of things. This seems to make it much more usable down to lower frequencies, although the manual is very generous in this regard, stating that it’s capable of reading down to 1kHz. In practice I’ve found the lowest it reliably reads the frequency input is 10MHz, using my AD9850 DDS VFO Module as a signal source.
It did however read slightly high on all readings with the DDS, but this could have been due to the low power output of the frequency source.
Just like the other frequency counter module, this also uses a trimmer capacitor to adjust the microcontroller’s clock frequency to adjust the calibration.
The power supply circuitry is in the bottom left corner of the board, in this case a small switching supply. The switching regulator is needed to boost the +4.5v of the batteries to +5v for the logic.
Also, as the batteries discharge & their terminal voltage drops, the switching regulator will allow the circuit to carry on functioning. At present I am unsure of the lower battery voltage limit on the meter, but AAA cells are usually considered dead at 0.8v terminal voltage. (2.4v total for the 3 cells).
When turned on this meter draws 52mA from the battery, and assuming 1200mAh capacity for a decent brand-name AAA cell, this should give a battery life of 23 hours continuous use.
On the back of the main PCB is a 5v relay, which seems to be switching an input attenuator for higher power levels, although I only managed to trigger it on the 2m band.
Finally, right at the back attached to an aluminium plate, is the 50Ω dummy load resistor. This component will make up most of the cost of building these, at roughly £15.
On my DVM, this termination reads at about 46Ω, because of the other components on the board are skewing the reading. There are a pair of SMT resistors, at 200Ω & 390Ω in series, and these are connected across the 50Ω RF resistor, giving a total resistance of 46.094Ω.
This isn’t ideal, and the impedance mismatch will probably affect the calibration of the unit somewhat.
The heatsinking provided by the aluminium plate is minimal, and the unit gets noticeably warm within a couple of minutes measuring higher power levels.
High power readings should definitely be limited to very short periods, to prevent overheating.
The RF is sampled from the dummy load with a short piece of Teflon coax.
There’s a rubber duck antenna included, but this is pretty useless unless it’s almost in contact with the transmitting antenna, as there’s no input amplification. It might be handy for detecting RF emissions from power supplies, etc.
For the total cost involved I’m not expecting miracles as far as accuracy is concerned, (the manual states +/-10% on power readings).
The frequency readout does seem to be pretty much spot on though, and the ability to calibrate against a known source is handy if I need some more accuracy in the future.
I’ve also done an SWR test on the dummy load, and the results aren’t good.
At 145.500 MHz, the SWR is 3:1, while at 433.500 it’s closer to 4:1. This is probably due to the lower than 50Ω I measured at the meter’s connector.
These SWR readings also wander around somewhat as the load resistor warms up under power.
I’ll probably also replace the AAA cells with a LiPo cell & associated charge/protection circuitry, to make the unit chargeable via USB. Avoiding disposable batteries is the goal.
Here’s a quick look at a Sainsmart frequency counter module. These are useful little gadgets, showing the locked frequency on a small LCD display.
It’s built around an ATMega328 microcontroller (µC), and an MB501L Prescaler IC. The circuit for this is very simple, and is easily traced out from the board.
Frequency Counter
Here’s the back of the board, with the µC on the left & the prescaler IC on the right. This uses a rather novel method for calibration, which is the trimmer capacitor next to the crystal. This trimmer varies the frequency of the µC’s oscillator, affecting the calibration.
Input protection is provided by a pair of 1N4148 diodes in inverse parallel. These will clamp the input to +/-1v.
The prescaler IC is set to 1/64 divide ratio. This means that for an input frequency of 433MHz, it will output a frequency of 6.765625MHz to the µC.
The software in the µC will then calculate the input frequency from this intermediate frequency. This is done because the ATMega controllers aren’t very cabable of measuring such high frequencies.
The calculated frequency is then displayed on the LCD. This is a standard HD44780 display module.
LCD
Power is provided by a 9v PP3 battery, which is then regulated down by a standard LM7805 linear regulator.
Readout
I’ve found it’s not very accurate at all at the lower frequencies, when I fed it 40MHz from a signal generator it displayed a frequency of around 74MHz. This is probably due to the prescaler & the software not being configured for such a low input. In the case for 40MHz input the scaled frequency would have been 625kHz.
As I’m building up my radio shack, I figured an SWR meter would be a handy addition to my arsenal. This is a cheap Moonraker brand meter, which also will measure RF power. Above the front of the meter is shown, with the moving coil meter movement on the left, calibration adjustment on the right & the forward/reverse power switch.
Meter Rear
For connections, standard SO-259 jacks are provided. The casing is sturdy 1mm steel. This is good, considering it’ll probably take a beating in my portable radio bag.
Directional Coupler PCB
Here the cover is removed, showing some of the internals. The large PCB across the back is the directional coupler.
Directional Coupler Circuit
The SO-259 connectors are bridged with a transmission line, (the track covered in solder in the image below), while there are a pair of sense lines running alongside. This main line is electromagnetically coupled to the two smaller sense lines, which are terminated at one end with resistors, with diodes at the other to rectify the coupled signal.
The termination resistors are sized to match the impedance of the sense lines.
The diodes, having rectified the coupled RF, produce DC voltages representing the value of the forward & reverse RF power. These DC voltages are smoothed with the capacitors.
PCB Marking
The PCB is dated 19-8-2011, so it’s a fairly old design.
Adjustments
Here is visible the back of the user calibration adjuster, with the factory calibration trimmer.
Meter Movement
Back of the meter movement. This is a standard moving coil type. Nothing special.
This meter will soon be modified to accept connection of an external Arduino-based SWR & power meter, which I can calibrate individually for each band.
Stay tuned for that upcoming project.
After watching a video over at Scullcom Hobby Electronics on YouTube, I figured I’d build one of these precision references to calibrate my multimeters.
It’s based around a REF102P 10v precision reference & an INA105P precision unity gain differential amplifier.
For full information, check out the video, I won’t go into the details here, just my particular circuit & PCB layout.
In the video, Veroboard is used. I’m not too fond of the stuff personally. I find it far too easy to make mistakes & it never quite looks good enough. To this end I have spun a board in Eagle, as usual.
Precision Ref SCH – Click to Embiggen
Here’s the schematic layout, the same as is in the video.
Precision Ref BRD
As usual, the Eagle CAD layout files can be found at the bottom of the post.
And the associated PCB layout. I have added the option to be able to tweak the output, to get a more accurate calibration, which can be added by connecting JP1 on the PCB.
As in the original build, this unit uses pre-built DC-DC converter & Li-Ion charger modules. A handy Eagle library can be found online for these parts.
I have however left off the battery monitor section of the circuit, since I plan to use a protected lithium cell for power. This also allowed me to keep the board size down, & use a single sided layout.
Toner Transfer Paper
Here’s the track layout ready to iron onto the copper clad board. I use the popular toner transfer system with special paper from eBay, this stuff has a coating that allows the toner to easily be transferred to the PCB without having to mess about with soaking in water & scraping paper off.
Ironed On
Here’s the paper having just been ironed onto the copper. After waiting for the board to cool off the paper is peeled off, leaving just the toner on the PCB.
Etched PCB
PCB just out of the etch tank, drilled & with the solder pins for the modules installed. Only one issue with the transfer, in the bottom left corner of the board is visible, a very small section of copper was over etched.
This is easily fixed with a small piece of wire.
Components Populated
Main components populated. The DC-DC converter is set at 24v output, which the linear regulator then drops down to the +15v rail for the reference IC. The linear section of the regulator, along with the LC filter on the output of the switching regulator produce a low-ripple supply.
SMPS Ripple
Here’s the scope reading the AC ripple on the output of the DC-DC converter. Scale is 100mV/Div. Roughly 150mV of ripple is riding on top of the DC rail.
Linear PSU Ripple
And here’s the output from the linear regulator, scale of 50mV/Div. Ripple has been reduced to ~15mV for the reference IC.
In total the circuit as built has a power consumption of ~0.5W, most of which is being dissipated as heat in the linear part of the PSU.
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