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by btidey
Sun Jan 12, 2020 9:37 am
Forum: Beginners
Topic: Pi Zero add Battery
Replies: 15
Views: 680

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: 680

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: 789

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: 789

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: 789

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: 789

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: 302

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: 337

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: 1128

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: 595

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: 13
Views: 1124

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: 13
Views: 1124

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: 13
Views: 1124

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: 13
Views: 1124

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: 13
Views: 1124

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: 740

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: 1474

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: 5106
Views: 1403857

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: 1339

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...
by btidey
Fri Apr 19, 2019 7:55 am
Forum: Automation, sensing and robotics
Topic: Voltage Datalogger (please help out a noob)
Replies: 6
Views: 826

Re: Voltage Datalogger (please help out a noob)

One idea to remove the problem of hazardous working is to use a plug in AC-AC power adapter that gives out a low voltage like 5V. It is important that it is AC output as that will be just an isolation transformer and not a regulated dc supply. It is also important to get one with a safety certificat...
by btidey
Thu Apr 11, 2019 7:06 am
Forum: General discussion
Topic: Use a Potentiometer to control sound.
Replies: 5
Views: 404

Re: Use a Potentiometer to control sound.

If you want a rotary control for the volume then consider using a rotary encoder instead of a potentiometer. An encoder can connect to a couple of GPIO pins and then rotation can be detected and turned into a 'value to control the volume digitally. Rotary encoders do not have an absolute position bu...
by btidey
Fri Mar 15, 2019 9:32 am
Forum: Beginners
Topic: Why my IR LED transmitter not transmit any signal?
Replies: 43
Views: 2376

Re: Why my IR LED transmitter not transmit any signal?

The original circuit is bad There is nothing specifically to limit the current drawn through the two diodes and the transistor. The voltage drop across an IR LED is about 1.5V so with 2 in series and a 5V supply the current will be determined just by the gain of the transistor and the capacity of th...
by btidey
Fri Mar 01, 2019 9:11 am
Forum: General discussion
Topic: Need an outdoor case for a security camera
Replies: 13
Views: 1966

Re: Need an outdoor case for a security camera

I want it to look like a CCTV camera though, because it's a visible deterrant. The original project I followed was here https://www.raspberrypi.org/blog/turn-your-pi-into-a-low-cost-hd-surveillance-cam/ however the dummy one suggested here is too small for the Pi3 (which has the micro USB power in ...
by btidey
Thu Feb 28, 2019 11:26 am
Forum: General discussion
Topic: Need an outdoor case for a security camera
Replies: 13
Views: 1966

Re: Need an outdoor case for a security camera

I think this one https://cpc.farnell.com/haydon/hay-772city/dummy-camera-external/dp/SR07209?MER=sy-me-pd-mi-alte would be big enough, but it's a pretty solid unit and expensive. This one also looks a possible https://www.ebay.co.uk/itm/Dummy-Security-CCTV-Camera-Quality-Aluminium-Fully-Weather-Proo...
by btidey
Thu Feb 07, 2019 9:20 am
Forum: General discussion
Topic: Does Raspberry Pi have enough power to control 50 LED's?
Replies: 6
Views: 482

Re: Does Raspberry Pi have enough power to control 50 LED's?

With that number of LEDs you should check out using WS2812B pixel LEDs. A single GPIO pin can control a whole string as they are wired in series. Each LED can be independently faded and have its colour set as each one is RGB. These LEDs are available as strips, circles, arrays or as individual dots....

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