Strength of reinforcement of nanovna-H connectors

The nanovna-H connectors are end launch PCB connectors and they have a decidedly spongy feel as 1Nm torque is approached. This was due to flexing of the PCB and was likely to lead to track cracks in the longer term.

Specs for SMA connectors range from minimum of 0.2Nm torque to maximum of 1.7Nm, but 0.6Nm and 1.0Nm are common commercial practice.

Above is a pic of a modification to reinforce the connectors. This article sets out the analysis of just the solder joint within the cross section of the brass pieces.

At first, the strength of the butt soldered joint might seem a simple case of beam analysis where the beam is of cast solder of the same cross section l x w as the soldered joint. Continue reading Strength of reinforcement of nanovna-H connectors

A mount for the coax relay driver development prototype

I was recently revising the code for the Coax Relay Driver to use a PIC16F1827 chip, and thought a good improvement would be a board that held the prototype electronics and the pulse latching relay together as an assembly.

Above is the design from Fusion360 to be cut from 3mm clear PVC sheet on the CNC router.

Above is the cut piece with four M3 heat melt threaded inserts for the electronics.

Above is the completed prototype assembly. The white cable to the left is an ICSP connection for programming / in circuit debugging of the code.

Whilst I used a CNC router do cut the board out, it could easily be done with a jigsaw and drill.

 

Normalised RMS voltage of a full wave phase controlled power waveform

The recent article Soldering iron – temperature control failure gave a plot of V’rms vs conduction angle for a simple full wave phase controlled AC waveform, and I have been asked to explain the derivation.

The phase controlled switch turns on at some delayed time from the zero crossing of the AC waveform, and conducts until the next zero crossing.

With the simplest circuits, there is a practical limit to the achievable stable range of conduction angle, and a minimum of about 50° to a maximum of about 160° is typical.

The RMS voltage is the square root of the mean of the square of the instantaneous voltage. We can write an expression for the normalised RMS voltage as a function of conduction angle θ. Continue reading Normalised RMS voltage of a full wave phase controlled power waveform

Soldering iron – temperature control failure

I wanted to modify a soldering iron to insert brass threaded inserts into holes drilled in plastic parts, and for this application looked to eBay for an inexpensive temperature controlled soldering iron that could be adjusted down to around 200°.

Well first check was of its temperature when set to 200°.

Ouch, that is a fail. The Chinese cheats have supplied product that does not comply with its description. Continue reading Soldering iron – temperature control failure

Acrylic plinth for small card modules – CNC router make

At Acrylic plinth for small card modules I described a contruction from sheet materials using a saw or score and snap.

In this article, I made a small plinth using the CNC router.

The design was created in Fusion 360 by importing a pic of the target module, calibrating it, and then laying up the plinth outline and the four holes. The first hole was dimensioned for diameter, then copied to the other three positions. Apart from dimensioning the first hole, all other design was visual.

Above is the design sketch. As a check, a dimension was take from the two widest spaced holes and compared with measurement of the actual board, and it was within 0.05mm. Continue reading Acrylic plinth for small card modules – CNC router make

CNC6040 router project – cut of enclosure for grbl_ESP32

One of the intended applications of the CNC router is to cut openings in metal and plastic enclosure boxes boxes for things like LCD displays, tactile button switches, connectors etc.

First ‘production’ job was a box to contain the grbl_ESP32 gcode interpreter, part of the CNC router if you like.

This module is the grbl_ESP32 box in the block diagram above. Continue reading CNC6040 router project – cut of enclosure for grbl_ESP32

CNC6040 router project – test cut of a Jiffy box

One of the intended applications of the CNC router is to cut openings in Jiffy boxes for things like LCD displays, tactile button switches, connectors etc.

After a lot of testing, it came time to try it on some target work.

Above is a scrap Jiffy box and the milling job is to cut holes for three pushbuttons (tactile momentary switches on a veroboard base with 10mm caps) and the holes for M3 screws and pillars. Continue reading CNC6040 router project – test cut of a Jiffy box

CNC6040 router project – spindle speed linearisation – using new grbl_ESP32 feature

A known issue with the common CNC6040 router and similar devices is very poor calibration / linearity of the spindle motor response to gcode Sx commands.

Above is the system block diagram. The grbl_ESP32 gcode interpeter processes a gcode S (speed) command, converting it to a variable duty cycle PWM waveform on parallel port pin 1. Continue reading CNC6040 router project – spindle speed linearisation – using new grbl_ESP32 feature

CNC6040 router project – spindle speed linearisation

A known issue with the common CNC6040 router and similar devices is very poor calibration / linearity of the spindle motor response to gcode Sx commands.

Above is the system block diagram. The grbl_ESP32 gcode interpeter processes a gcode S (speed) command, converting it to a variable duty cycle PWM waveform on parallel port pin 1. Continue reading CNC6040 router project – spindle speed linearisation