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by PiGraham
Tue Aug 14, 2018 9:27 am
Forum: Troubleshooting
Topic: Data capture via GPIO
Replies: 7
Views: 113

Re: Data capture via GPIO

How many channels do you intend to use at what sample rate, for how long? What do you intend to do with the data? at 8 channels and 110kHz that's 2.64 Mbytes/s which may be possible but I think you would have to sample asynchronously and find the sync pulses in the data. You might also need to de-se...
by PiGraham
Mon Aug 13, 2018 8:15 am
Forum: Beginners
Topic: How to detect an old style wired doorbell only - nothing else
Replies: 20
Views: 369

Re: How to detect an old style wired doorbell only - nothing else

Did you know that you are providing approximately - 0.8V to the input of your ESP8266 ;) . Instead of this: A resistor / zener diode clips this so a 0 - 3.3V 50 Hz pulse is fed into a GPIO pin. However, I find you code interesting and I need to take a closer look at it. Yes. That is true. It was lo...
by PiGraham
Sat Aug 11, 2018 10:40 pm
Forum: Automation, sensing and robotics
Topic: How to read motor's tach out open collector
Replies: 1
Views: 64

Re: How to read motor's tach out open collector

Connect Pin 4 tacho to a gpio input, connect the GND pin between motor interface and Pi and set a pullup. Set a callback on the input to cout up each time the tach line pulses low.
by PiGraham
Sat Aug 11, 2018 8:41 am
Forum: Beginners
Topic: How to detect an old style wired doorbell only - nothing else
Replies: 20
Views: 369

Re: How to detect an old style wired doorbell only - nothing else

Useful circuits Brandon92.
It isn't essential to rectify ac or filter 50/100Hz since it is possible to handle a pulse train in software. So you could leave out D1 to D4 and C3 and C2.
The opto will turn on every other half cycle and if there are any no pulses in 20ms the bell is not pressed.
by PiGraham
Fri Aug 10, 2018 6:49 pm
Forum: Beginners
Topic: How to detect an old style wired doorbell only - nothing else
Replies: 20
Views: 369

Re: How to detect an old style wired doorbell only - nothing else

rpdom wrote:
Fri Aug 10, 2018 5:43 pm
The reason for the opto is to filter out any interference that the long leads may pick up. The opto-isolator is a lot less sensitive than a GPIO.
It will also protect the Pi from any high voltage spikes that can be produced by electromagnetic bells.

Sounds like a nice setup you have there.
by PiGraham
Fri Aug 10, 2018 3:18 pm
Forum: Beginners
Topic: How to detect an old style wired doorbell only - nothing else
Replies: 20
Views: 369

Re: How to detect an old style wired doorbell only - nothing else

https://electrical.knoji.com/images/user/danmsnyder/doorbell-transformer-wiring-fbdaee2c.jpg Is the transformer could be ac or dc. Can you check? Basically you can connect and opto-isolator across the bell terminals and connect the output to a gpio. Connect it like a push button. Choose a series re...
by PiGraham
Wed Aug 08, 2018 2:02 pm
Forum: Advanced users
Topic: How to sense my smartphone in a room
Replies: 5
Views: 179

Re: How to sense my smartphone in a room

If you keep Bluetooth or WiFi on you can detect if your phone is in range of another device. If you have admin access to a WiFi rounter in your room you could check the DHCP list on the router for your phone. Check the RSSI levels on two or more radios to locate the phone. If you pair a Pi3B+ with t...
by PiGraham
Wed Aug 08, 2018 9:44 am
Forum: Camera board
Topic: Picamera with custom lens, color issue
Replies: 3
Views: 124

Re: Picamera with custom lens, color issue

Corrections are applied for the standard lens. The issues are discussed here:
viewtopic.php?t=168777

You can get the raw pixel values and apply your own Bayer processing and colour corrections for still images.
by PiGraham
Mon Aug 06, 2018 6:14 pm
Forum: Python
Topic: I need help with an LDR
Replies: 11
Views: 243

Re: I need help with an LDR

I'm not convinced about the logic behind the opening and especially the closing of the door. Sounds much too easy to have a situation in which the door closes when the car is not fully clear of the doorway. Excellent point. At least two sensors are required. One to detect approach and one to detect...
by PiGraham
Mon Aug 06, 2018 4:39 pm
Forum: Python
Topic: I need help with an LDR
Replies: 11
Views: 243

Re: I need help with an LDR

You can use an LDR for this sort of thing but an alternative might be better. I suggest you do not rely on daylight to illuminate the LDR because that can vary a lot. Use an LED light to shine a beam across the space where the car will go. You can have a solution that is less sensitive to daylight v...
by PiGraham
Mon Aug 06, 2018 4:26 pm
Forum: Beginners
Topic: using PI with 2 serail ports?
Replies: 3
Views: 69

Re: using PI with 2 serail ports?

USB serial interfaces are cheap and effective to I'd go that way, but DMA controlled software serial on any gpio pin is another option.

viewtopic.php?t=35544#p446164

http://abyz.me.uk/rpi/pigpio/cif.html#gpioWaveAddSerial
by PiGraham
Mon Aug 06, 2018 7:05 am
Forum: Beginners
Topic: Will sharing keyboard & mouse between Pi and PC require Pi reboot?
Replies: 6
Views: 172

Re: Will sharing keyboard & mouse between Pi and PC require Pi reboot?

You might find it more convenient to use VNC or SSH to view the Pi desktop or SSH to use the command line from your PC without changing connections.

Plugging and unplugging USB devices doesn't require a reboot though, so you can do that if you prefer.
by PiGraham
Sun Aug 05, 2018 3:56 pm
Forum: General discussion
Topic: Tranquility Project
Replies: 61
Views: 1878

Re: Tranquility Project

Seems that it would be easier to hitchhike a ride to the ISS and send it on its way from there. The problem then being getting there, the entry, Getting a tiny experiment module delivered to the ISS is worlds away from getting a launch system deployed from the ISS. Your enthusiasm is commendable bu...
by PiGraham
Sun Aug 05, 2018 3:52 pm
Forum: Troubleshooting
Topic: MOSFET switch is leaking current when off
Replies: 15
Views: 350

Re: MOSFET switch is leaking current when off

Why do people seeking help so often refuse to provide basic information or try simple tests?
A neat diagram is a good thing, but much better to show the actual circuit in a photo. Then we aren't confounded by getting the diagram wrong (100k /10k) we see what you actually used.
Help us to help you.
by PiGraham
Sat Aug 04, 2018 3:37 pm
Forum: Troubleshooting
Topic: MOSFET switch is leaking current when off
Replies: 15
Views: 350

Re: MOSFET switch is leaking current when off

It might help to see exactly the circuit connections and code being used.
by PiGraham
Fri Aug 03, 2018 8:57 am
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

@PiGraham My point was more the use of the pi. If he want to make in total 50 units. I think it is a overkill way to use a pi to control only 4 Leds. And the cost are indeed not the leds itself. It may be that the Pi is doing something much more involved than just lighting LEDs. The OP gives no clu...
by PiGraham
Fri Aug 03, 2018 7:08 am
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

If you need more light use lower value resistors from 3.3V There is no call (but no harm) for using additional transistors to switch these small LEDs. The GPIO can easilly supply ten times the current you estimate to be " in the neighbourhood of 1mA" I agree, if he has the skills and tools to solde...
by PiGraham
Thu Aug 02, 2018 9:47 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

If you need (much) more light you will need a transistor to switch the LED on (with VCC = 5V). transistors with integrated gate resistors do exist, but are rare and expensive, a simpler/cheaper solution would be to use a FET, like a 2N7000 no extra resistor needed. Remember only to use a FET that t...
by PiGraham
Wed Aug 01, 2018 6:33 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

stmulligan wrote:
Wed Aug 01, 2018 6:22 pm
My plan was one pin/one LED per GPIO. Seems I'm back where I started - not sure whether or not to try and drive this bar from GPIO.
You are 100% safe using 3.3V to Vcc.
by PiGraham
Wed Aug 01, 2018 6:28 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

You shouldn't connect 5V to gpio but here the LEDs will drop at least 1.7V so the gpio will not see more than 5 - 1.7 = 3.3V when the output is off so that should be OK. When the LED is on the pin voltage will be close to zero, of course. Use 3.3V if that works for you or use 5V if needed. Well I'm...
by PiGraham
Wed Aug 01, 2018 3:07 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

drgeoff wrote:
Wed Aug 01, 2018 2:42 pm
8 LEDs = 24 mA. total maximum.
Could be, although 24mA seems more likely to be the max rating of a single LED
by PiGraham
Wed Aug 01, 2018 3:05 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

Yes, they light fine by grounding the individual S pins, but I was told that using GPIO pins to ground devices is not a good idea (hence the topic title). By backwards logic, I meant that my original design drove 4 LEDs by setting a GPIO pin high to the already grounded LED. This inverts that logic...
by PiGraham
Wed Aug 01, 2018 1:58 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

That board looks likes this https://www.ebay.co.uk/itm/24mA-8Pcs-LED-Bar-Marquee-Display-Module-With-4-Kinds-of-Color-for-Arduino-RH/292651566302?hash=item44236484de:g:86wAAOSwUC1bVUlY That says 24mA 5V Assuming 2V forward voltage across each LED that implies 125R series resistors. (5V - 2V)/24mA = ...
by PiGraham
Wed Aug 01, 2018 1:46 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

Yes, I have no problem wiring up individual LEDs. My issue is that I'm moving from breadboards to field units. I need to make about 50 and they each have 4 LEDs. That's a lot of soldering so I bought a handful of these LED Bars. http://powerchalk.info/wp-content/uploads/2018/08/ledbar.jpg Only to r...
by PiGraham
Wed Aug 01, 2018 12:24 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 780

Re: GPIO as GND

From my readings, I assume that I need an NPN transistor - meaning I send low power to the base to supply ground to the LED. Can someone point to a suitable part# or ebay listing with a built in resistor on the base pin? I'm assuming the resistor needs to be 10K. You can drive small LEDs directly. ...

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