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by Earlton2
Sun May 10, 2020 2:22 am
Forum: Beginners
Topic: [SOLVED] How to run a gphoto2 command on start up?
Replies: 8
Views: 268

Re: How to run a gphoto2 command on start up?

I use systemctl to start up a program via a script call and a systemctl timer to periodically send a signal to the latter for data capture. The script with the embedded Signal can also be called from the Terminal so it makes it useful for testing. I'm not saying you need Signals or even program star...
by Earlton2
Mon May 04, 2020 12:14 am
Forum: Teaching and learning resources
Topic: Car nut would love some guidance for a car computer. Not sure where to look
Replies: 4
Views: 434

Re: Car nut would love some guidance for a car computer. Not sure where to look

The 5/3.3V conversion just works as a ratio so 2.5V in would simply give 1.65V etc. It's normal intent is to prevent a 5V device from hurting a 3.3V Pi or peripheral chip. If your sensors generated 12V then a 12/3.3 ratio would be required. I'm presently using an Analogue to Digital device with an I...
by Earlton2
Tue Apr 14, 2020 9:30 pm
Forum: Assistive technology and accessibility
Topic: Where do i start
Replies: 4
Views: 474

Re: Where do i start

DietPI, PI-Top, Noobs_V3 ? As an example I use "C" with system calls to espeak. static char sEmerg[200] /* a string for the emergency message */ ... /* build up the espeak command and throw the resulting file at aplay */ sprintf(sEmerg, "espeak -ven-uk-north -a50 -p10 -s150 --stdout" " \" Am bulance...
by Earlton2
Mon Apr 13, 2020 10:49 pm
Forum: Beginners
Topic: Anemometer
Replies: 38
Views: 1283

Re: Anemometer

For calibration don't you just stick it out of the car window and take a few regulated runs down a country lane. A co-pilot might be a good idea!
by Earlton2
Sat Apr 04, 2020 2:08 pm
Forum: Automation, sensing and robotics
Topic: Values in the ADC are fluctuating and incorrect.
Replies: 9
Views: 402

Re: Values in the ADC are fluctuating and incorrect.

Does this have anything to do with big-endian, little-endian interfacing. I had to swap bytes when doing A2D on my RaspberryPi. I am using WiringPi to run the i2c not a Python driver or such.
by Earlton2
Thu Mar 26, 2020 8:25 pm
Forum: Beginners
Topic: emulate a Printer
Replies: 1
Views: 96

Re: emulate a Printer

I'm hopeful you get some answers to your query as we have an old LED display which I've interface to a RPi over the serial lines. If the Pi would look like a printer to an Ethernet line then we could add it as a teaching aid to a library network . At the moment it 'speaks' ASCII, EBCDIC and Baudot. ...
by Earlton2
Tue Jan 28, 2020 10:28 pm
Forum: Weather station
Topic: Rainfall Sampling
Replies: 5
Views: 496

Re: Rainfall Sampling

The rainfall detector appears to toggle both ways so the switch will be on or off for the time taken to fill the 'bucket'. You read the switch in one of your loops (say 5-min) i.e. ON or OFF. When the new reading is different from the old one increment the rainfall count, after which you save old = ...
by Earlton2
Sun Jan 19, 2020 3:09 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Serial on RPi B works; won't work on RPi Zero W
Replies: 4
Views: 384

Re: Serial on RPi B works; won't work on RPi Zero W

In raspi-config I set: 1. Interface > Serial > ... login .. accessible over serial > NO 2. ... serial port hardware to be enabled > YES I'm using WiringPi to access serial: if (wiringPiSetup() == -1) .... if ((ftmp = serialOpen ("/dev/serial0", baud)) < 0) << part of set-up, int ftmp - file descript...
by Earlton2
Wed Jan 15, 2020 11:05 pm
Forum: Automation, sensing and robotics
Topic: Device to measure angle for input to RPI
Replies: 3
Views: 342

Re: Device to measure angle for input to RPI

Inclinometers et al: https://www.digikey.ca/products/en/sensors-transducers/motion-sensors-inclinometers/533?FV=-8%7C533&quantity=0&ColumnSort=1000011&page=1&k=tilt&pageSize=25 C$35 ++ over here. Also used in game controllers so maybe some much cheaper parts are available. You'll have to go hunt for...
by Earlton2
Tue Jan 14, 2020 1:50 am
Forum: Beginners
Topic: UART Alarm system control suggestions
Replies: 7
Views: 596

Re: UART Alarm system control suggestions

10 cents: DETECTING SIGNAL LEVELS 1. The driver/receiver of RS232 is an inverter so the TTL level is the inverse of the RS232 levels. 2. A serial line is usually marking unless there is data or something sending break. 3. Marking on the TTL line is +ve, (Pi GPIO-14/15 = 3.3V), spacing on the TTL lin...
by Earlton2
Thu Jul 04, 2019 12:44 am
Forum: General discussion
Topic: A question about power
Replies: 7
Views: 477

Re: A question about power

Might be of interest but not supporting the amps required for a Pi-4: My supply for a CNC machine uses two 12V PC power supply boards in series and I use the first 12V to provide 5V through a 7805 regulator (1.5A). This tends to get a tad hot but is surviving. The stepper driver circuit was doing th...
by Earlton2
Tue Jun 04, 2019 10:08 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Is it possible to communicate with my ultrasonic flow meter
Replies: 1
Views: 401

Re: Is it possible to communicate with my ultrasonic flow meter

I have used wiringpi to set-up drive the serial port. The actual wiring usually needs an inverting driver between the pi logicand the device rs232. Nominally the latter is +/- 12v but more often than not it uses 0 to 5v levels. You might check the device TD pin when marking (idle) to see if it is 0 ...
by Earlton2
Wed Apr 17, 2019 1:15 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: I2C RTC DS1337 1Hz clock on SQW/INTB RS1 RS2 EOSC
Replies: 1
Views: 498

Re: I2C RTC DS1337 1Hz clock on SQW/INTB RS1 RS2 EOSC

I am still using a DS1337 for my RTC but using rtc-ds1307 inside /boot/config.txt There are still additional registers available on the chip and specifically for me 0x0E with the RS1/2 bits at 0x18. To my surprise I now find I can set these with i2cset -f -y -m 0x18 1 0x68 0x0E 0x00. This outputs a ...
by Earlton2
Sun Mar 17, 2019 1:49 am
Forum: Other projects
Topic: Power for outoor enclosure
Replies: 4
Views: 1080

Re: Power for outoor enclosure

I'd use a 12V line if that will power both devices with 7805 regulator to generate 5V into the Pi on the GPIO lines. There are also pin compatible switchers with the same footprint but less heat. My set-up uses a 12V trickle charged battery to provide power for several devices scattered around the h...
by Earlton2
Fri Mar 01, 2019 4:04 pm
Forum: Automation, sensing and robotics
Topic: Cat Home DIY Q&A - Solenoid How To
Replies: 35
Views: 4193

Re: Cat Home DIY Q&A - Solenoid How To

its likely of no significance in this circuit but the led diode in the transistor base will slow down the base discharge and delay the turn off. i.e. placing the transistor in linear mode. if anything i would suggest adding a 4k7 to gnd at the base.
by Earlton2
Thu Feb 28, 2019 6:38 pm
Forum: Automation, sensing and robotics
Topic: Water Depth Sensing
Replies: 10
Views: 4007

Re: Water Depth Sensing

on sonar units we used a pressure sensor. these were analog current loop so we had to use a converter inside the unit. a loop allows you to have a long cable but the sensor has to be fixed on the bottom not just hung over the side. arduino is the usual suggestion here but i would tend to wire up an ...
by Earlton2
Thu Feb 14, 2019 1:31 am
Forum: General discussion
Topic: Is Raspberry Pi capable of replacing 2 wire thermostat
Replies: 8
Views: 1129

Re: Is Raspberry Pi capable of replacing 2 wire thermostat

then again you could use a standard thermostat in the control circuit and use a relay closure or ac switching device across it. the thermostat could be set at a safe default minimum e.g. 10c while the new circuit runs the weekly sequence. the pi needs to get time from either the web or an rtc.
by Earlton2
Thu Feb 14, 2019 1:10 am
Forum: General discussion
Topic: Powering RPi inside of PC case
Replies: 17
Views: 4912

Re: Powering RPi inside of PC case

i would mount the pi on a piece of wood that slides into an empty harddrive slot. the nuts on db25 and de9 connectors make a good standoff with 4-40 bolts. re power i tend to run 5v and ground into the gpio connector using a 10-pin header at pos-1 . for simple projects this gets me i2c and tx/rx whi...
by Earlton2
Mon Feb 11, 2019 9:38 pm
Forum: Advanced users
Topic: EMULATION HELP REQUEST
Replies: 13
Views: 1515

Re: EMULATION HELP REQUEST

I don't understand a word of it but having started with a PDP-8 in the 1960's with a DMA college project, I'm enjoying the ride. The other computer was a LEO with a door on the back so you could get inside and change the valves!
by Earlton2
Wed Jan 30, 2019 10:07 pm
Forum: Wanted
Topic: RPi, 26 pin GPIO and Mounting Holes
Replies: 9
Views: 3142

Re: RPi, 26 pin GPIO and Mounting Holes

Would it help to simply purchase a Pi-Zero sans pins and solder in the 26 you need? Or purchase a 40-pin Pi and chop off the unwanted pins. The Pi's don't care. I often just solder in a 10-pin header on a Pi-zero. The top position (pin-1) gets you power, I2C and serial data which is sufficient for s...
by Earlton2
Tue Jan 29, 2019 3:04 am
Forum: General discussion
Topic: What is the temperature range of model A?
Replies: 16
Views: 4985

Re: What is the temperature range of model A?

No idea but I presently have a Zero-W running in an unheated building where outside temperatures of late have reached -41C. The processor shows 2C while the plastic case it sits inside is down to -16C. Other than the CPU, all probes are TMP107s with the outside units attached to a bat house. Data ca...
by Earlton2
Mon Jan 21, 2019 2:10 am
Forum: Beginners
Topic: Detect electrical current of external device
Replies: 13
Views: 1395

Re: Detect electrical current of external device

The attached schematic shows two opto-couplers, two 2.2K resistors and two 1N914 diodes wired to the bell circuit and interfaced with a Pi. There are separate inputs for FRONT and REAR which need limiting to around 10mA for the opto device. The diodes are to protect the opto devices from reverse vol...
by Earlton2
Mon Dec 10, 2018 4:58 pm
Forum: Beginners
Topic: how to increase the raspberry pi 3 wifi range
Replies: 9
Views: 14261

Re: how to increase the raspberry pi 3 wifi range

My simple reflector antenna is cut from cardboard with aluminum foil strip stuck to the inside. It is 400 mm across and 50 mm high with no attempt to make the short vertical parabolic. The equation I used was y = x*x/4f with x from 0 to +/-200 mm and focus f at 100 mm. The f value was chosen so the ...
by Earlton2
Fri Nov 30, 2018 2:20 am
Forum: Assistive technology and accessibility
Topic: Dementia clock/picture frame and audio suggestion for my mum, best practice?
Replies: 7
Views: 7515

Re: Dementia clock/picture frame and audio suggestion for my mum, best practice?

Could you split the code into separate tasks which could be called by system control timers. i.e an 8 a.m. call to whatever needs doing then. I have several systemctl 'functions' one of which starts a program and another which periodically sends a signal to trigger a data sample. I'm afraid it would...
by Earlton2
Fri Nov 30, 2018 2:04 am
Forum: General discussion
Topic: High Wattage Remote Relay
Replies: 12
Views: 1237

Re: High Wattage Remote Relay

I've pulled many a relay from old microwave ovens and furnaces. Much of these have the power lines on top as spade lugs while the low voltage coil lines were soldered to the board on the bottom. Early on the coils were 12V but of late they are more likely 24VDC. In either case I have used a 2N2222 t...

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