Go to advanced search

by PiGraham
Fri Sep 24, 2021 9:34 am
Forum: General discussion
Topic: easiest way to find pins on the GPIO header without counting?
Replies: 32
Views: 1251

Re: easiest way to find pins on the GPIO header without counting?

scruss wrote:
Wed Sep 22, 2021 7:45 pm
Pi Supply used to make colour-coded headers for the Zero, but haven't seen them in a while.
I don't know who makes them but :
https://thepihut.com/products/colour-coded-gpio-headers

Image
by PiGraham
Fri Sep 17, 2021 12:53 pm
Forum: SDK
Topic: Is it safe to call different member functions of one objects from different cores?
Replies: 10
Views: 357

Re: Is it safe to call different member functions of one objects from different cores?

If you literally only need to pass one int value between cores you don't need a mutex. The write and read will be atomic. It's where you pass data that spans multiple cycles that you risk reading part way through a write. I don't know the detail but I'm sure the two cores accessing shared memory mus...
by PiGraham
Thu Sep 09, 2021 7:52 am
Forum: General
Topic: Low-latency pattern matching peripheral data
Replies: 12
Views: 497

Re: Low-latency pattern matching peripheral data

The key qustion is what timing reference point are you trying to trigger at? If the target runs code to put some bytes into a transmit FIFO, which then go into a UART Tx shift register, there is no way to detect the time of that target code execution from the inherently delayed bitstream on the ser...
by PiGraham
Wed Sep 08, 2021 12:47 pm
Forum: Beginners
Topic: Table Tennis Highlight System / Instant replay
Replies: 4
Views: 209

Re: Table Tennis Highlight System / Instant replay

It seems this is mostly a question about GoPro.
by PiGraham
Wed Sep 08, 2021 11:41 am
Forum: General
Topic: Low-latency pattern matching peripheral data
Replies: 12
Views: 497

Re: Low-latency pattern matching peripheral data

I don't know much about glitching attacks but I gather one objective is to disrupt individual instruction cycles. How would that work triggering from a slow asynchronously clocked multi-byte UART bitstream to target a specific CPU instruction cycle running at much higher frequency? Is the assumption...
by PiGraham
Wed Sep 08, 2021 7:44 am
Forum: General
Topic: Low-latency pattern matching peripheral data
Replies: 12
Views: 497

Re: Low-latency pattern matching peripheral data

The problem here is that even if data is coming from a 9.6kbaud UART, typically, an instruction running on the target is what is being targetted, not another byte being sent. The target does some peripheral access (UART/SPI/I2C/...), and a bit afterwards, it runs the sensitive code that should be g...
by PiGraham
Tue Sep 07, 2021 4:14 pm
Forum: General
Topic: Low-latency pattern matching peripheral data
Replies: 12
Views: 497

Re: Low-latency pattern matching peripheral data

Can you get the system under test, either at the Tx or Rx end of the serial link, to output a low latency trigger that has a meaningful relation to the operation?
by PiGraham
Tue Sep 07, 2021 3:20 pm
Forum: General
Topic: Low-latency pattern matching peripheral data
Replies: 12
Views: 497

Re: Low-latency pattern matching peripheral data

What latency do you need? What sort of patterns do you need to detect? Basically "as low as possible" :) For patterns it's just comparing bytes that are coming in from a UART/SPI/I2C/... I think you should try to put a number on it. If you have asynchronous serial bitstream coming in at 9...
by PiGraham
Tue Sep 07, 2021 9:57 am
Forum: General
Topic: Low-latency pattern matching peripheral data
Replies: 12
Views: 497

Re: Low-latency pattern matching peripheral data

What latency do you need?
What sort of patterns do you need to detect?

I see the ChipWhiserer is an open source FPGA based device.
Built-in serial port for communications and programming STM32Fx targets.
Can you utilise that serial port?
by PiGraham
Tue Sep 07, 2021 7:28 am
Forum: Beginners
Topic: Control 10 wires with 5v
Replies: 13
Views: 460

Re: Control 10 wires with 5v

Thank you very much, no, I will use one by one, so I need only transistors/relay board, can I power this board from 5v pin on GPIO? No. Well.. you can probably power the board itself from the Pi's 5v, but you definitely cannot also use that 5v and pass it through to the controlled devices. Actually...
by PiGraham
Mon Sep 06, 2021 8:24 pm
Forum: Beginners
Topic: Control 10 wires with 5v
Replies: 13
Views: 460

Re: Control 10 wires with 5v

Always will be used one wire as output but I have to control which wire. I'm not makinf specific recomendations here, merely pointing to examples of the sort of devices that may be useful to you. If you want to enforce the exclusive 1 of N active you could use a demultiplexer. https://cdn.shopify.c...
by PiGraham
Mon Sep 06, 2021 11:25 am
Forum: Other projects
Topic: Screenly OSE -- Digital Signage for the Raspberry Pi
Replies: 1139
Views: 464398

Re: Screenly OSE -- Digital Signage for the Raspberry Pi

Hi, I'm trying to resurrect the use of Screenly in our school. We have 3 devices that are set up, however I only have IP addresses for the remote management of 2 of them. Any suggestions on how to find the IP address of the third device would be great. I'm hoping that it has the same username and p...
by PiGraham
Wed Sep 01, 2021 3:56 pm
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

In some ways the easiest of all options is to shorten the screen to whatever length you want and unroll it in/out all the way.
It does depend how the screen mechanism detects the in/out stop conditions but there's a fair chance that will work just the same with a shorter screen.
by PiGraham
Wed Sep 01, 2021 3:18 pm
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

These are all terrible ideas, but please don't let me stop you. Have you ever tried open loop time based positional control of a projector screen, most likely driven by a motor with no speed regulation? How accurate do you think it will be? Desired accuracy hasn't even been hinted at but clearly it...
by PiGraham
Wed Sep 01, 2021 10:02 am
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

I really wish there were a way to check and see if it were extended or to keep track of whether it was partially open, all open, fully closed, or in position. There might be way to do that. The RFID sticker (or QR code or barcode) on the back of the screen could give you a position confirmation. A ...
by PiGraham
Tue Aug 31, 2021 9:24 am
Forum: Python
Topic: GUIZERO and random
Replies: 1
Views: 169

Re: GUIZERO and random

I am trying to make a Magic Eight Ball app using guizero. I created images for each possible message in a separate file within my app. I was using random.choice to pick an answer after the user clicks the PushButton. I was playing around with it, but think the main issue is I can't use the variable...
by PiGraham
Tue Aug 31, 2021 8:26 am
Forum: Beginners
Topic: Read midi signals to move a servo
Replies: 2
Views: 164

Re: Read midi signals to move a servo

Possible? Yes, I think so.
Detailed howto? I don't know.
To get you started you might look at:
Pygame.midi.
https://www.pygame.org/docs/ref/midi.ht ... midi.Input

To move a servo look at gpiozero.servo
https://gpiozero.readthedocs.io/en/stab ... html#servo
by PiGraham
Tue Aug 31, 2021 8:17 am
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

BTW, I don't recommend this but you can get through-beam optical sensors that trigger when the beam is broken. You could use such a sensor with it's beam set so that the bottom of the screen breaks it at 7/8ths drop. Search IR gate sensor or light barrier. There are some cheap devices out there with...
by PiGraham
Tue Aug 31, 2021 8:14 am
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

Apologies. That was a bit blunt. However, you've had lots of suggestions, and lots of people want to see your project succeed. So, what are you going to do, and do you need specific help with it? At this point, I'm finishing something I thought would be finished a week or more ago, but I frequently...
by PiGraham
Mon Aug 30, 2021 8:53 pm
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

Put it all in a little box on the screen unit. Neat and tidy without extra wiring. While that box would be visible, it would be "harmless" if done right - it's something I could do easily. That could detect when the white reflective part of the screen appeared and when it disappeared agai...
by PiGraham
Mon Aug 30, 2021 11:17 am
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

That RJ45 may offer an even simpler option.
If there the RJ45 interface has a stop input you could wire an IR sensor direct, or via a timer to give a pulse, so that the screen stops itself at the mark. No programming.
by PiGraham
Mon Aug 30, 2021 10:41 am
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

This is very complex. If the screen is controlled by IR remote you can get a Pi to signal IR control codes. See LIRC If there's a permanent 12V feed to the screen unit you can tap into that to feed the Pi via a DC-DC Buck converter that outputs 5V 2A Put ths Pi0 with a basic IR sensor ( typical exam...
by PiGraham
Sat Aug 28, 2021 10:22 pm
Forum: Beginners
Topic: How to deal with many buttons with Raspberry Pi (Zero W)?
Replies: 19
Views: 795

Re: How to deal with many buttons with Raspberry Pi (Zero W)?

The clock just makes for easier timing for the data. WS2812 with just the data requires precise timing to drive it because the duration of the data pulse resets the chip. In practice there are good libraries to drive these LEDs reliably even from user code in Linux. So no fancy extra features from 6...
by PiGraham
Sat Aug 28, 2021 6:51 pm
Forum: Automation, sensing and robotics
Topic: Controlling a Projection Screen and Sensing Its Position
Replies: 62
Views: 2385

Re: Controlling a Projection Screen and Sensing Its Position

simplest option i can see, to avoid having the sticker get rolled up and deforming the screen on the other side, is to just not have the sticker in a rolled up part if you slap it on the bar at the bottom, it will just never enter the roll! But then you have to have a sensor far away from the roll,...

Go to advanced search