Wind sensor using car reversing kit

In reply to https://hackaday.io/project/181677/discussion-169393

I  had  another  look at the mcu that I removed from my 2nd version of the car reversing kit and saw it had  chip markings on the underside. (N.B 2 pictures shown as for some reason the light obscures one or other dependent on angle )The markings say:

   FH511
   LON.1

However I couldn't find anything useful by googling that!

Here also are some closeups of the two footprints on the 2 different car reversing kit boards I have.

mcu footprint of first kit1 I bought

mcu footprint of second kit I bought

Here is why I think it might be a PIC12

The original MCU pinout ( based on the 8 pin footprint, but for both boards) v PIC12 footprint. I have only quickly studied the PIC12 datasheet and the pcb so data may be inaccurate!

Schematic for ESP-01 web server allowing the wind data to to be presented in real time on a web page. 

Transmit out to Arduino is not used at the moment, but would be a nice option, if you can fit it on the board, so one day Sensor could be configured from web interface.  ArduinoRST goes to the Arduino reset line. RXI is the wind sensor data from the Arduino using a voltage divider (not shown here) (2.2K / 3.3K resistors) to drop the voltage to 3.3V. NPN transistors could be used instead of mosfets Q6 Q7, but they would need bases to be connected to 3.3V via (say) 10K resistors. The mosfets were selected because they use slightly fewer components. Voltage regulator should ideally be a TO220 or similar with a good heat-sinking capability as it has quite a voltage drop, when powered from 12V and the ESP-01 does use 100 mA or so when in WiFi transmission mode. R32 is required to prevent the ESP-01 starting in programming mode. Adding a reset button to ESP-01 is always a useful feature too!

TODO.

• Do a video describing more details of the circuit and how it fits on the car reversing kit PCB.

• Update github project with sub-modules to include required web server libraries.

• Explain how to upload code to ESP-01 etc

Source code for the web server  here:

https://github.com/kwikius/ultrasonic_wind_sensor/blob/master/web_server/web_server.ino

Update the add on board with ESP-01. Once added to the board Initially I found that ESP-01 had difficulty connecting to the network. I suspect that it is due to noise on the hacked PCB , since connection works fine, if the Arduino is held in reset.  That being the case, I solved the problem by connecting the ESP-01 GPI0 to the Arduino RST input ( via suitable level shift). Now When ESP-01 wishes to connect , it puts Arduino in reset and takes Arduino out of reset once connected. This works well as a solution on the demo board. Once connected the Wifi is smart enough to avoid the noise frequencies and the connection seems to be robust enough for testing and demonstrating.

https://github.com/kwikius/ultrasonic_wind_sensor/blob/master/web_server/web_server.ino#L105

TODO: Provide circuit details for ESP-01 and a video of the updated board

The windsensor project is very critical on interrupt timing  to capture the pulse length. Looking at the Arduino.Serial code, it does (of course) use interrupts and even disables the global interrupts during a write. In this application a simple polled serial port will do the job without globally disabling interrupts and without serial write interrupt getting in the way of the envelope detect or zero crossing interrupts, so the Arduino code was modified to use the custom polledSerial class.

https://github.com/kwikius/ultrasonic_wind_sensor/blob/master/libraries/polled_serial/polled_serial.cpp

Added video and info on how to hook up the Arduino to the extended car reversing kit pcb

To get the project working originally I used an external comparator. The comparator is used first to measure the magnitude of the received pulse stream and then to detect zero crossing, by means of positive feedback which moves the trip level between the two levels dependednt on output state

I wanted to use the internal comparator and eleiminate theat extra component. One problem with the internal comparator is that the outout doesnt go to a pin, which means the traditional positive feedback cant be used. I originally decided to use a spare pin as an output and use it to set positive feedback to the input it in the comparator interrupt, but then I realised I could just use 2 different comparator channels and switch between them in the comparator interrupt.  After some headscratching  and layout issues this is now working well and I plan to stick with this option for the moment. This is actually a much nicer option since it doesnt put any load on the output and samples the filter ground directly rather than a voltage which is around the same level as I was doing with the external comparator. I also would hope that the settling time is much reduced since both of the negative outputs have constant values, one at filter ground and one at envelope detect voltage and the filter output is not loaded at all.

I also got v2 of the circuit working using the car reversing pcb in the videos, which is much neater than V1, so now need to do a new video about it all.

Modify source code so that we don't need to disable interrupts. Important since the comparator  is meant to have a lot of positive feedback, which has to be done in software in an interrupt, while only around 6 usec is available to flip the output.
https://github.com/kwikius/ultrasonic_wind_sensor/commit/9627a261ac55dd3647f3f7eb349310b97648b39b

The existing 8 pin soic mcu has to be removed. I have a hot air soldering iron for this task. (If you don't have one, then it is possible to remove smd ics by making a u shaped piece of thick copper wire and soldering it to the ic's pins with blobs of solder. Heat it up with a bigish soldering iron and then pull it off with tweezers)

Also shown in the video is  the piece of proto board, attached to the existing pcb with double sided tape, which works much better than you would think..

Cut out and fitted the proto board to add some area to the original PCB.

In the video I mention knitting the 2 boards together with copper wire. To line up the boards for drilling, I  joined the board with doubles sided tape. Once done, I discovered that the result was strong enough just using the tape, which makes life much easier.  Next todo is to remove the MCU with a hot air soldering iron, so will see if the proto board falls off with the heat!

Added comparator circuit to circuit description.