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by stevend
Wed May 16, 2018 9:07 pm
Forum: General discussion
Topic: Effective way to communicate Raspberry Pi with STM32
Replies: 13
Views: 4041

Re: Effective way to communicate Raspberry Pi with STM32

If you're going to use serial, I suggest you at least consider RS-422. Using differential signalling, it has much better noise immunity than RS-232, and can operate over much longer distances, although that's unlikely to be an issue for you here. A device from the MAX3483-MAX3491 group would do the ...
by stevend
Tue May 15, 2018 12:34 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Does anyone know of an I2C device that just deals with the interfacing?
Replies: 16
Views: 903

Re: Does anyone know of an I2C device that just deals with the interfacing?

Bear in mind that the total length of an I2C bus is limited (something like 500mm, IIRC). It sounds as if this might not be enough for your application, in which case you'll need a method of communicating over longer distances - networking being a simple option. (Also look at MQTT for the actual 'pr...
by stevend
Thu May 03, 2018 10:10 pm
Forum: General discussion
Topic: GPIO - sensing wire break
Replies: 13
Views: 744

Re: GPIO - sensing wire break

If you get an analog to digital converter, the problem becomes much simpler. You can signal a number of states according to the amount of resistance in the circuit. IIRC there's a similar thread related to intruder alarms somewhere. Basically have three resistors A, B, C in series: Resistor A from y...
by stevend
Tue Apr 24, 2018 12:39 pm
Forum: Automation, sensing and robotics
Topic: Various Devices on Home Network
Replies: 2
Views: 276

Re: Various Devices on Home Network

Have a look at home automation systems; many of them will interface to a variety of devices. The two I'm looking at for my next system are Domoticz and OpenHAB It's also worth installing an MQTT broker (which can possibly run on the same processor as other bits of the system) - a very flexible way o...
by stevend
Sun Apr 22, 2018 7:20 am
Forum: General discussion
Topic: Recommend GPIO expander (like PCF8574) but default/initial state is not input?
Replies: 2
Views: 456

Re: Recommend GPIO expander (like PCF8574) but default/initial state is not input?

Most, if not all, configurable I/O devices will power up with the I/O pins set as inputs. You need to pick one with an option of push-pull outputs, where you can configure the pins to outputs during startup without momentarily glitching them high. IIRC the MCP23008 that Trevor suggested would do thi...
by stevend
Fri Mar 30, 2018 7:27 am
Forum: Automation, sensing and robotics
Topic: Light sensor for RPi3 that sends notifications
Replies: 3
Views: 834

Re: Light sensor for RPi3 that sends notifications

There are really two parts to your project, which you can deal with one at a time. The first is to get the (internal) signal which indicates 'on' or 'off' - and it sounds as if you've already got that sorted. The second part is to send the message. Find an example project where this part works the w...
by stevend
Sun Mar 18, 2018 11:20 pm
Forum: Automation, sensing and robotics
Topic: Campervan sensors?
Replies: 12
Views: 1568

Re: Campervan sensors?

Should I start buying these things or stick to woodwork?! Neither! Do some more research first. Plenty of comment on these forums. I think you could have responded with a 'stick to woodwork' (not that I'm great at that, either!). Clearly you're one of the internet's gentlemen. Thanks! Hopefully you...
by stevend
Sun Mar 18, 2018 9:16 am
Forum: Automation, sensing and robotics
Topic: NPN Photoelectric Sensor - Output Not Going Low
Replies: 17
Views: 1580

Re: NPN Photoelectric Sensor - Output Not Going Low

According to the data sheet, the sensor's 'Output Voltage' is 2V max at 100mA. So I wonder whether the output stage is actually a Darlington transistor. (Industrial stuff is often designed to work with higher voltages). You could try replacing the 56K resistor of pcmanbob's circuit with the emitting...
by stevend
Sun Mar 18, 2018 9:06 am
Forum: Automation, sensing and robotics
Topic: Campervan sensors?
Replies: 12
Views: 1568

Re: Campervan sensors?

Should I start buying these things or stick to woodwork?! Neither! Do some more research first. Plenty of comment on these forums. You've got it right that you'll need an A-D converter for much of what you want to do; the one you've found looks unnecessarily good (and correspondingly costly). Somet...
by stevend
Wed Mar 07, 2018 1:32 pm
Forum: General discussion
Topic: Short stroke linear actuator
Replies: 4
Views: 848

Re: Short stroke linear actuator

Have a look at the ones intended for moving domestic satellite dishes to point to another satellite. They come in a variety of sizes. The ones at http://www.thesatelliteshop.net/c-band-satellite-satellite-dish-actuator-c-715_837.html look relatively costly to me, but should give the idea. There are ...
by stevend
Thu Mar 01, 2018 8:21 pm
Forum: Automation, sensing and robotics
Topic: Lowest latency way to send picamera frames (numpy array) over LAN for OpenCV analysis?
Replies: 18
Views: 2592

Re: Lowest latency way to send picamera frames (numpy array) over LAN for OpenCV analysis?

https://www.pyimagesearch.com/2017/09/04/raspbian-stretch-install-opencv-3-python-on-your-raspberry-pi/ worked for me - you do have to follow the instructions exactly! (One or two of the packages have been updated since that post was written, and there's no problem using the latest as long as you re...
by stevend
Wed Feb 28, 2018 1:45 pm
Forum: Automation, sensing and robotics
Topic: Lowest latency way to send picamera frames (numpy array) over LAN for OpenCV analysis?
Replies: 18
Views: 2592

Re: Lowest latency way to send picamera frames (numpy array) over LAN for OpenCV analysis?

You could maybe approach the problem from a different angle. Establish an accurate reference clock at each Pi, and keep them in sync. Then tag each set of data with the time. This way the latency doesn't greatly matter, as long as the average throughput is adequate. Note: When I say 'accurate' for t...
by stevend
Fri Feb 16, 2018 8:24 pm
Forum: Automation, sensing and robotics
Topic: Send serial command immediately on pin change, avoiding serial conflicts
Replies: 1
Views: 349

Re: Send serial command immediately on pin change, avoiding serial conflicts

It depends a bit on your definition of "immediate". However I think you'd be unwise to attempt to terminate a Modbus transaction part way through; you'd need to implement timeouts and things to ensure everything had recovered, and that could well be slower than letting any current transaction take i...
by stevend
Sun Feb 11, 2018 8:08 am
Forum: Other projects
Topic: Looking for design guidance
Replies: 4
Views: 754

Re: Looking for design guidance

If the Pi is just managing the display, and accessing an existing database to get the data (i.e. data acquisition is handled by some other device) a single app, in the sense of a single thread, will be fine. Then I suggest using classes and inheritance to display the data; a base class for the core,...
by stevend
Thu Feb 01, 2018 9:59 pm
Forum: General discussion
Topic: Wireless Gate Switch
Replies: 2
Views: 278

Re: Wireless Gate Switch

The 'fuse box' probably contains some electronics to control the gate motors and so on. If you get the installation manual (look inside for the manufacturer and model number if there's no other way - watch out for mains!), you may find that the unit has several control inputs which control the gates...
by stevend
Wed Jan 24, 2018 1:38 pm
Forum: Automation, sensing and robotics
Topic: Location and bearing of a stationary setup
Replies: 2
Views: 413

Re: Location and bearing of a stationary setup

Money, programming, and welding are not unlimited but I'd like the bearings to be about 0.05 degrees accurate...! I would say you're being very optimistic! (at least unless you've got lots of money) To get a reference bearing you'll need some sort of compass (a GPS only gives position when stationa...
by stevend
Mon Jan 15, 2018 1:59 pm
Forum: Automation, sensing and robotics
Topic: Simple Counter / Trawl Monitoring
Replies: 1
Views: 370

Re: Simple Counter / Trawl Monitoring

A couple of comments. Firstly, your general idea of using a pulley seems sound; however I think you'll need either a different pulley, or a separate wheel that the wire runs over. You need something with enough friction between wire and pulley wheel to ensure you get an accurate measurement. And som...
by stevend
Fri Jan 05, 2018 6:27 pm
Forum: General discussion
Topic: Web server for RasPi 3?
Replies: 23
Views: 4336

Re: Web server for RasPi 3?

Hi all Thanks for the replies. Why would be creating the webserver in pascal be weird - my program is written in pascal!!! I am all for KISS! Brian Have you looked at the Indy offerings? IIRC they include a web server. (Or you could do direct comms using sockets - might even be easier!) http://wiki...
by stevend
Wed Dec 20, 2017 1:50 pm
Forum: Off topic discussion
Topic: Cellular Connected Home Phone System
Replies: 5
Views: 3221

Re: Cellular Connected Home Phone System

Search for "GSM Analogue Gateway" - that throws up various cellular-connected devices with a standard UK phone socket to plug a phone into (available for other countries too, but for some reason I've assumed you're in the UK). For example: http://www.gsmgateway.co.uk/product-category/gsm-gateways/an...
by stevend
Wed Dec 13, 2017 10:01 pm
Forum: Automation, sensing and robotics
Topic: Beginner - Automation of Outside Christmas Lights
Replies: 60
Views: 6076

Re: Beginner - Automation of Outside Christmas Lights

Phase 2 - incorporate temperature sensors. The old thermostat is still in use, but would value people's opinions on what's possible here. Nice to be able to measure the temperature in different zones - e.g upstairs & downstairs - although I realise, with my current setup, I can't control the heatin...
by stevend
Mon Dec 11, 2017 1:16 pm
Forum: Automation, sensing and robotics
Topic: Beginner - Automation of Outside Christmas Lights
Replies: 60
Views: 6076

Re: Beginner - Automation of Outside Christmas Lights

It's a shame as a year and a bit ago it was in pieces, what with a same size again extension and full heating and electrics needed. (It's a bungalow). At least you can put a lot in the loft space; possibly you might get useful readings with sensors on the ceiling (although the temperatures would, I...
by stevend
Sun Dec 10, 2017 10:08 pm
Forum: Automation, sensing and robotics
Topic: Beginner - Automation of Outside Christmas Lights
Replies: 60
Views: 6076

Re: Beginner - Automation of Outside Christmas Lights

Sorry Steve - the 3 hours in the cold garage has frozen my brain - I'm not 100% sure I understand what I need to do here. I've tried to sketch what I currently have in place (I've left off neutral and ground wires for ease). Can you point me in the right direction on the diagram. The squares with 2...
by stevend
Sun Dec 10, 2017 5:45 pm
Forum: Automation, sensing and robotics
Topic: Beginner - Automation of Outside Christmas Lights
Replies: 60
Views: 6076

Re: Beginner - Automation of Outside Christmas Lights

some of the wires weren't long enough You may have seen the red (and blue and yellow) crimps that are used for joining wires; they're handly for extending short wires, and will sit happily in the junction box without taking up much space. Best to go for the ratchet crimp tool; you'll get more relia...
by stevend
Sat Dec 09, 2017 4:06 pm
Forum: Automation, sensing and robotics
Topic: Beginner - Automation of Outside Christmas Lights
Replies: 60
Views: 6076

Re: Beginner - Automation of Outside Christmas Lights

The wire in the top leftt is actually the frost stat, so that means the Hall thermostat is feed up via the conduit!? That actually makes more sense, since the hall is presumably a short distance away? So there should be several wires going up that conduit: 1. A T&E (twin and earth) taking power to ...

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