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by stevend
Fri Apr 18, 2014 8:29 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: MCP3008 with or without optocoupler
Replies: 37
Views: 8052

Re: MCP3008 with or without optocoupler

Using the 3.3V supply as a reference for the A-D will work, but might not give you the repeatability/accuracy you want. Power supplies tend to be noisy, so as a minimum isolate the reference input using a small inductor and a 100uF capacitor. Also, PSU voltages and regulation with temperature are va...
by stevend
Wed Apr 16, 2014 5:07 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Data diode (unidirectional comm) between 2 RPis
Replies: 28
Views: 11382

Re: Data diode (unidirectional comm) between 2 RPis

The constant current idea won't quite work as described - you will end up with variable voltage. As soon as the Pi takes some current, the current through the parallel resistor will drop, so (using Ohm's law) the voltage across it will decrease - quite possibly to a level where the Pi stops working....
by stevend
Wed Apr 16, 2014 12:51 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: MCP3008 with or without optocoupler
Replies: 37
Views: 8052

Re: MCP3008 with or without optocoupler

A good way to protect the Pi is to isolate digitally between the Pi and the A-D - it won't matter that the A-D circuitry is connected to the ground of your battery. (And bear in mind that the battery may not be connected to 'true ground' , i.e. 'earth' - it may also be floating). As well as normal o...
by stevend
Mon Feb 03, 2014 1:33 pm
Forum: Automation, sensing and robotics
Topic: Pi Based Tide clock/display
Replies: 16
Views: 4431

Re: Pi Based Tide clock/display

So with tides having a period of 12.5 hours it would be simple to equate this to counting a 1 PPS signal from a GPS receiver. If you get the period between high tides accurate, this would certainly work - essentially an electronic version of the 'tidal clocks' mentioned earlier. The most accurate t...
by stevend
Thu Jan 30, 2014 6:09 pm
Forum: Automation, sensing and robotics
Topic: Pi Based Tide clock/display
Replies: 16
Views: 4431

Re: Pi Based Tide clock/display

The interval between successive high tides is usually around 12.5 hours. In an ideal world the tide height against time is a sinusoidal curve; local effects change this, with the Solent being particularly non-sinusoidal - you get a double high water in places. (see http://www.ntslf.org/data/realtime...
by stevend
Sat Oct 12, 2013 9:16 pm
Forum: Automation, sensing and robotics
Topic: Room by Room central heating control
Replies: 31
Views: 30895

Re: Room by Room central heating control

What I would love is to be able to retrofit valves to the radiators that allowed me to turn specific rooms on and off. Some of the electronic thermostatic valves might be a good basis for this, since they fit onto a standard radiator valve with M30 thread - relatively straightforward and economical...
by stevend
Fri Oct 11, 2013 4:56 pm
Forum: Automation, sensing and robotics
Topic: Room by Room central heating control
Replies: 31
Views: 30895

Re: Room by Room central heating control

just a quick comment on the valves, I know that some boilers will keep the pump running after they cut the flame to stop itself over heating. So its common for a system to have some sort of bypass fitted or one rad that can't be switched off to give somewhere for the water to flow. It's easy to see...
by stevend
Fri Oct 11, 2013 4:54 pm
Forum: Automation, sensing and robotics
Topic: Room by Room central heating control
Replies: 31
Views: 30895

Re: Room by Room central heating control

I looked at these valves too, because they look promising, but for zone control I find them to be of no use because of the long cycle time, off->on is somewhere in the region of a few minutes, which is the length of time a lot of my programs are on for Bear in mind that the 'response time' of affec...
by stevend
Fri Oct 11, 2013 12:39 pm
Forum: Automation, sensing and robotics
Topic: Room by Room central heating control
Replies: 31
Views: 30895

Re: Room by Room central heating control

I'm part way through implementing a similar system, and thought I'd mention my approach to the radiator valves, which is slightly different. I'm buying the http://www.conrad-electronic.co.uk/ce/en/product/615952/Honeywell-Rondostat-HR20-Radiator-Thermostat Honeywell HR20 electronic thermostatic valv...

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