Programming a certain type of Chinese 315/433MHz EV1527 compatible remote relay

This article describes the programming sequences for a common Chinese 315/433MHz remote relay which works with the common EV1527 transmitter.

The EV1527 should not be confused with high security protocols, the transmitter has burned into it four fixed supposedly relatively unique codes (in a space of 1 million code possibilities) and sends the burned in code associated with the transmitter key each time it is operated. This should not be confused with rolling code systems such as KeeLoq. This information is not usually disclosed by sellers.

These are usually supplied with little or no instructions, or bad online translations that are quite misleading. I dare say sellers have refunded money in lots of cases due to user confusion about programming them or compatible transmitters. This information might assist owners to find a working solution.

Above is an example remote relay (~$3 on eBay), they are available with a number of channels and may look physically different but use the same or similar firmware. Note that though the relay on this one is rated at 10A AC, that rating is for resistive load and it is rated at 5A AC for an inductive load (PF=0.4). Continue reading Programming a certain type of Chinese 315/433MHz EV1527 compatible remote relay

Reinforcement of nanoVNA-H connectors – performance discussion

At Strength of reinforcement of nanoVNA-H connectors I showed a method I used to reinforce the SMA connectors to reduce the flexing of the PCB when the SMA connectors were torqued to specification for reliable measurement.

This has been commented on by online experts stating that Hugen, the designer of this board, posted notes about his efforts to keep the grounds for tx and rx port circuits isolated to some extent.

Opinion by some is that the modification I performed above which electrically bonds the two connectors through a brass bar of about 60mm length is likely to significantly degrade performance. Continue reading Reinforcement of nanoVNA-H connectors – performance discussion

Chinese wattmeter / power analyser fix

I bought a little wattmeter / power analyser with SB50 style plugs on it on eBay for about $20.

These devices have been common in the RC market for many years, and I have found them useful for a number of things but note that the input -ve lead is NOT directly connected to the output -ve lead, you cannot use them where the input -ve and output -ve are common.

 

The problems

Above is the promo pic. Of course they are not Anderson plugs, but clones. Continue reading Chinese wattmeter / power analyser fix

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.

Some nanoVNA sellers state:

As the SMA ports are made of cast copper, please not connect hard 50-7 / RG213 and other cables directly to the SMA ports through M-to-SMA connector to avoid damaging the SMA ports. You can use the included SMA cable to connect to the SMA port as shown in the picture below, and then use M to SMA connector.

Clearly Chinese Cheats, they will say anything to make a sale and anything to avoid commitment to quality. These connectors are very unlikely to be copper, but are likely to be a copper alloy: brass. What they also avoid in the above statement is claim for PCB damage due to flexure of the SMA connectors torqued to accepted industry torque for reliable connections and measurement.

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.

A side effect is that this modification bonds the ground planes for the input and output parts of the nanoVNA via the brass bar where they have been kept isolated to some extent.

I should note that there has been much discussion online as to whether the noise floor of the nanoVNA is degraded by the shields fitted to the board, and various modifications to the shields. Some of this discussion proposes that the issue is mostly around the mixers and noise loops, and I note that in -H designs prior to v3.3, the mixer power supply was not adequately decoupled. It is possible that electrical connection of the SMA connectors in this way degrades noise performance at some frequencies. No significant change was observed in the noise floor of s11 or s21 channels from 1 to 300MHz (I don’t regard instrument performance to be good above 300MHz). I have not seen credible evidence of degradation of the nanoVNA-H v3.3 build.

If indeed bonding the two SMA connectors close to the instrument increases the noise floor or has other performance impacts as suggested, it questions whether the currents on the exterior of the coax influence measurement (which it should not) and it questions whether two port measurement fixtures or adapters should  be attached close to the nanovna.

(See also Reinforcement of nanoVNA-H connectors – performance discussion.)

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