PCB Oscilloscope & PSU Module

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Geoff Theasby G8BMI has a PCB oscilloscope for around £10 and a variable voltage module for just £3.

 

 

Geoff Theasby G8BMI has a PCB oscilloscope for around £10 and a variable voltage module for just £3.

 

This oscilloscope is not a project for the beginner! It contains several surface-mount components 2 x 1.2mm (0805) on a compact PCB, 80 x 115mm, with a display piggy-backed on. One 48-leg IC is presoldered for you (Phew!). A few test points need to be shorted with solder after setup but the copper foil is very thin and can peel off if treated badly. I prefer to use a thin bare wire to bridge them; a cut-off resistor leg will do. The instructions are the best I’ve yet seen, in full colour, on glossy paper, with circuit and full test results and setup details. The project took me eight hours of slow and careful construction, checking carefully, testing voltages and so on, in order to achieve success. Make sure you get the JYE Tech, red, PCB kit to avoid a common counterfeit. Three resistors were left over and one was missing, fulfilled from my stock. With a maximum input of 200kHz, this is not for RF work but is nevertheless a versatile tool for the bench and even comes with its own oscilloscope probe. The unit requires a supply of 12V maximum, at 200mA. It costs about £10.

Stage 1: insert surface mount components. These measure 2 x 1.2mm and are held with tweezers, soldered in place. If you place all resistors the same way round and right way up, this makes it resemble a project built by a competent constructor. A dozen such components took two hours to fit, aided by a large magnifier, good lighting and steady hands. This last I do not have... A hands-free magnifier is a great help, as is a jeweller’s loupe.

Stage 2: leaded resistors. These are colour coded, with which I am familiar, but again so small that I have to check their resistance with a (digital) test meter (No, it isn’t futile!). The rest of the components are routine to fit, making sure they are on the correct side of the PCB and observing polarity.

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Detailed setup notes and basic usage instructions are provided, including probe calibration. There is a small amount of residual noise on the display, making it look a little ‘hairy’, but what do you expect for a tenner? In the photo it is displaying an output from the Function Generator (PW November 2017).

 

Variable Voltage Module

Using an LM317 IC on a small heatsink and controlling a maximum current of 2A, the built module this month is an adjustable voltage regulator for £3. An awkwardly-placed two-digit seven-segment display shows voltage out (above 3V) and the input can be 20V AC or 30V DC. The board contains a bridge rectifier. A single potentiometer adjusts the voltage out, which can range from 1.25V to 28V at 2A. Very useful for a bench power supply, if fed with an old CB 12V power supply, ‘wall wart’ or transformer. The voltage out could be better displayed by attaching an outboard 3½ digit LED voltmeter, which are often available at rallies for £1.

 

This article was featured in the October 2018 issue of Practical Wireless