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by btidey
Thu Oct 08, 2020 10:03 am
Forum: Automation, sensing and robotics
Topic: Hardware needed for temperature sensor
Replies: 2
Views: 191

Re: Hardware needed for temperature sensor

You can set up the raspberry headless without needing a keyboard, screen, mouse, LAN cable (using wifi) etc. if you have access to another computer then you can login via ssh, and even do remote desktop access.

https://www.raspberrypi.org/documentati ... eadless.md
by btidey
Sat May 02, 2020 8:30 am
Forum: Automation, sensing and robotics
Topic: 433MHZ sniffer - External Light Switch
Replies: 8
Views: 981

Re: 433MHZ sniffer - External Light Switch

First don't be fulled by getting any sort of results from the receiver. All receivers have an agc circuit which means the gain is turned right up with no signal present so they put out random 1's and 0's even with no signal. They will put out decent data when a signal is transmitted and the gain is ...
by btidey
Thu Feb 27, 2020 12:48 pm
Forum: Automation, sensing and robotics
Topic: 18650 and Raspberry pi 4 connecting.
Replies: 4
Views: 477

Re: 18650 and Raspberry pi 4 connecting.

You can feed %v directly into the expansion header, but take care as this bypasses protection circuitry. So you need to make sure the supply is within range and you get the polarity right.
by btidey
Sat Feb 22, 2020 9:34 am
Forum: General discussion
Topic: MOSFET vs BJT for Pi Relay Circuit
Replies: 8
Views: 826

Re: MOSFET vs BJT for Pi Relay Circuit

I do normally use MOSFET as logic switches to get better characteristics (lower voltage drop when on, less heat, easier driving). I don't use the 2N7000 series though. Although the threshold is fairly low (2.5V) this is when the device just starts to conduct. Like a lot of MOSFETS the 2N7000 only ha...
by btidey
Sun Jan 26, 2020 11:10 am
Forum: Automation, sensing and robotics
Topic: Take over thermostat 868 MHz RF signal
Replies: 5
Views: 720

Re: Take over thermostat 868 MHz RF signal

Working out the existing protocol will give the neatest solution, but might prove to be difficult. If you get stuck another mechanism is to make use of the existing unit if the boiler manual on off works as you indicate. I assume there are some buttons for the manual controls so you could then use t...
by btidey
Thu Jan 23, 2020 11:24 am
Forum: Automation, sensing and robotics
Topic: Detect lockout state of garage door?
Replies: 2
Views: 359

Re: Detect lockout state of garage door?

You could use a photo-transistor next to the LED (reasonably shielded from any other strong lights). Emiiter to 0V, Collector to GPIO and pulled up to 3.3V through say 100K resistor. LED on gives GPIO low, LED off gives GPIO high. You then need to detect the difference between steady on and flashing...
by btidey
Sun Jan 12, 2020 9:37 am
Forum: Beginners
Topic: Pi Zero add Battery
Replies: 15
Views: 1062

Re: Pi Zero add Battery

I agree PI is not always best choice for long term battery operation. AVR and PIC are in a different class with an infinitely smaller drain. But very hard to implement IOT. ESP draws 10x more and the sleep part has issues but wifi programming a lot easier. Pi easiest of all to implement network but...
by btidey
Fri Jan 10, 2020 6:49 pm
Forum: Beginners
Topic: Pi Zero add Battery
Replies: 15
Views: 1062

Re: Pi Zero add Battery

If you want to collect weather data and use a battery to power it then you will probably be better off using the Pi as a server to store the weather data but use a microcontroller with low power consumption and deep sleep capability to actually interface to the sensors and communicate the results ba...
by btidey
Sun Dec 15, 2019 3:44 pm
Forum: Automation, sensing and robotics
Topic: Choosing NPN BJT as a switch for RPI to control motor by PWM
Replies: 15
Views: 1300

Re: Choosing NPN BJT as a switch for RPI to control motor by PWM

First on Vbe 2n3055 specification. That is shown as the Vbe when 1/10 of collector current is used (to keep it saturated). Although the base emitter behaves like a diode, there is also a resistive component (internal leads, connection through the silicon). At low and medium currents the diode drop i...
by btidey
Thu Dec 12, 2019 3:51 pm
Forum: Automation, sensing and robotics
Topic: Choosing NPN BJT as a switch for RPI to control motor by PWM
Replies: 15
Views: 1300

Re: Choosing NPN BJT as a switch for RPI to control motor by PWM

The 0.7V for Vbe is not a constant. The base emitter behaves just like a diode. So it starts conducting significantly when more than 0.5V is applied to it and then the current increases by 10 fold for every extra 60mV applied. So an extra 180mV increases the current by 1000. The relatively small cha...
by btidey
Wed Dec 11, 2019 8:35 am
Forum: Automation, sensing and robotics
Topic: Choosing NPN BJT as a switch for RPI to control motor by PWM
Replies: 15
Views: 1300

Re: Choosing NPN BJT as a switch for RPI to control motor by PWM

The primary starting point for a BJT is that Vce must be kept low when On otherwise it is not a good switch. The beta drops off at low Vce as the cb junction becomes slightly forward bias so the collection of current is less effective. This means you have to have to provide more base current than si...
by btidey
Tue Dec 10, 2019 11:19 am
Forum: Automation, sensing and robotics
Topic: Choosing NPN BJT as a switch for RPI to control motor by PWM
Replies: 15
Views: 1300

Re: Choosing NPN BJT as a switch for RPI to control motor by PWM

1. Yes The motor should be the determining factor for the current drawn. That means you want the switch (BJT or MOSFET) to be able to pass that the maximum possible without significant voltage drop across it. 2. Don't worry about motor resistance in this case. You need to focus on keeping the switch...
by btidey
Mon Dec 02, 2019 8:39 am
Forum: Automation, sensing and robotics
Topic: Interfacing Raspberry PI with HoneyWell Sensor
Replies: 2
Views: 479

Re: Interfacing Raspberry PI with HoneyWell Sensor

That sensor has a 1 -5 Vdc analog output across the airflow range. You would need an ADC input for the raspberry Pi. There are several HATs available that would do the job. The sample rate and accuracy requirements are not high but you would need one that can convert across the 0 - 5V range. The sen...
by btidey
Sun Nov 17, 2019 9:27 am
Forum: Automation, sensing and robotics
Topic: How to turn on Multiple TVs using a raspberry Pi?
Replies: 4
Views: 590

Re: How to turn on Multiple TVs using a raspberry Pi?

If each TV is fed from a PC then you could drive the local IR diode from the PC I believe lirc can drive a diode via the DTR line of a serial port. Then either the PC locally turns the TV on when its is rebooted or you send network commands to the PC to do it from a central point. The other thing to...
by btidey
Sat Nov 02, 2019 9:02 am
Forum: Automation, sensing and robotics
Topic: Triggering an Alarm with a Raspberry Pi
Replies: 11
Views: 1892

Re: Triggering an Alarm with a Raspberry Pi

Also note that in some countries there are noise pollution regulations that require a time out on alarm sounders like this. In the UK this is a maximum of 20 minutes, although many modern alarm bells have a built in limit of 15 minutes. If you are using a software controlled dumb siren then you shou...
by btidey
Tue Oct 08, 2019 8:17 am
Forum: Automation, sensing and robotics
Topic: Looking for a relatively low-cost electrical conductivity sensor that gives the signal in digital output
Replies: 5
Views: 1150

Re: Looking for a relatively low-cost electrical conductivity sensor that gives the signal in digital output

You need to give a bit more info to get some suggestions. What type of material are you trying to measure; liquid, solid? What range of conductivity are you trying to measure? What accuracy are you trying to achieve? Conductivity is normally measured by sensing the current flow across a known geomet...
by btidey
Mon Oct 07, 2019 8:05 am
Forum: Automation, sensing and robotics
Topic: Dimming fluorescent lights
Replies: 17
Views: 1848

Re: Dimming fluorescent lights

To get a more linear response you could use a simple look up table to translate the desired dim power into the value of PWM needed. You might also want to play around with the pwm set up. Higher frequency is good to ensure the capacitor smooths out the signal to avoid flicker but also reduces the re...
by btidey
Sun Oct 06, 2019 8:22 pm
Forum: Automation, sensing and robotics
Topic: Dimming fluorescent lights
Replies: 17
Views: 1848

Re: Dimming fluorescent lights

Looking at the picture it seems the 470 resistor is shorted out the same way as you had on the input. That would mean even a low value of pwm would discharge the capacitor very quickly as the opto transistor turns on leading to the low voltages you see. Try correcting that. The value of the 470 resi...
by btidey
Sun Oct 06, 2019 9:48 am
Forum: Automation, sensing and robotics
Topic: Dimming fluorescent lights
Replies: 17
Views: 1848

Re: Dimming fluorescent lights

Few things. 1. Keep PWM frequency as high as possible. This is second parameter of IO.PWM. Maybe use 2000. 2. I would leave the 100K value. That should set maximum brightness when PWM is 0. 3. Sounds like PWM is not getting through for some reason. You can do a first level check by monitoring the vo...
by btidey
Thu Oct 03, 2019 9:16 pm
Forum: Automation, sensing and robotics
Topic: Dimming fluorescent lights
Replies: 17
Views: 1848

Re: Dimming fluorescent lights

I thought about using the op-amp approach but the snag is that the + is not really a voltage supply so you need a separate 10V power supply and then it states that one should isolate the output from the micro-controller which makes it tricky. The servo approach would work fine and provides isolation...
by btidey
Thu Oct 03, 2019 11:55 am
Forum: Automation, sensing and robotics
Topic: Dimming fluorescent lights
Replies: 17
Views: 1848

Re: Dimming fluorescent lights

I don't think a digital potentiometer is the best method here. The 10V interface is actually more like a current sink interface. The + is a supply voltage fed through a resistor, The analog potentiometer from here to - means that the voltage at the + will drop as the potentiometer is reduced in valu...
by btidey
Sun Sep 08, 2019 8:00 am
Forum: Automation, sensing and robotics
Topic: safe protocol for cheap 433MHz transceiver
Replies: 8
Views: 1230

Re: safe protocol for cheap 433MHz transceiver

Depending on what your PIC is doing another thought would be to replace that with a wifi module like an ESP8266 based unit (Wemos D1 or ESP-12F). The ESP8266 can do most things a PIC can do. The wifi range is very good without external aerials; the processor is fast; the modules are very cheap; and ...
by btidey
Mon Aug 12, 2019 8:26 am
Forum: Automation, sensing and robotics
Topic: Anyone built successfully RF receiver and transmitter on pi3
Replies: 3
Views: 5909

Re: Anyone built successfully RF receiver and transmitter on pi3

You really do need an antenna on both receiver and transmitter. You can get pre-wound little coil antennae which are OK or a straight 17cm wire will work OK. Stick with the second superhet receiver. They are much better than the regnerative type in the first link. Verify that your curtain remote is ...
by btidey
Fri Jul 05, 2019 6:42 pm
Forum: Camera board
Topic: RPi Cam Web Interface
Replies: 5244
Views: 1584256

Re: RPi Cam Web Interface

Any timeline as to when the installation script will be updated to take into account the new Buster build? Just installed RPi Cam on Buster, no problems, weirdly it will not now install on Jessie!!! The script now calls for php7.3 to be installed this is not available on earlier versions, if you lo...
by btidey
Fri Apr 19, 2019 3:23 pm
Forum: Automation, sensing and robotics
Topic: Can a power line provide Raspberry Pi and a lamp with power?
Replies: 16
Views: 1784

Re: Can a power line provide Raspberry Pi and a lamp with power?

I know there have been lots of articles about neat wifi 6 features helping IoT but ... ax is not even ratified yet, (Q3 2019?) some pre-ratification products are only just starting to appear (Samsung 10), and your router will need an upgrade. A lot of IOT is quite usable today without the extra feat...

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