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1  Using Arduino / Programming Questions / Re: Flash Memory of Arduino Uno on: August 26, 2014, 01:57:21 pm
Uno has 0.2 Mbyte, just 2K,  2048 bytes, of SRAM.

Sorry, 2k = 0,002M ..  smiley-small
2  Using Arduino / Programming Questions / Re: Help wanted: Controlling multiple OpenTherm thermostats with one Arduino on: August 26, 2014, 01:01:11 pm
Both thanks for answering.
@Mark: I've seen this FSM, have googled it, but what it's doing is not quite obvious to me. When you say this will do the job, I'll have a second look at it.
@Robin, I will see if I can make a schematic of what should (or could) happen with the 6 thermostats bit sequences. Give me some time to work things out.

3  Using Arduino / Programming Questions / Help wanted: Controlling multiple OpenTherm thermostats with one Arduino on: August 25, 2014, 02:52:54 pm
An OpenTherm (OT) thermostat controls a boiler with a 32 bits command.
This command is sent by Manchester coding.
There are a few topics about handling the code and the commands, e.g.
- (software)
- (hardware)
- (all about interrupts)

Above helped me to make an Arduino controlled OT gateway, which is working fine.
For the final step in my home automation project, I need to control 6 OT thermostats (each room has its own thermostat).
At this point it becomes quite complicated, maybe some can help me out!

The facts:
- with OT, the thermostat is master, the boiler (or now: Arduino) is slave
- there's no way to control the thermostat via Arduino: Arduino is only answering at questions of the master
- each bit (of total of 32 +2 start/stop bits) takes 1msec
- because of manchester coding, a level change could occur at 500 microseconds
- the thermostat is communicating once in a second
- within 800msec, the slave has to answer the master
- the slave MUST anwer the master (otherwise the master stops communicating)

The problem:
Above was possible with one thermostat. But I encountered lots of problems with multiple (6) thermostats:
- each thermostat acts as a master, which means that different commands of different thermostats arrives 'mixed up' in Arduino (e.g.: when handling bit 17 of thermostat One, startbit of thermostat 2 is incoming).
- while controlling incoming commands, I have to generate an answer for the resp. thermostat, as well controlling the boiler and heating zones.
(- for even more fun, I have to calculate a parity bit for each command)
- finally, I need I2C to communicate with the rest of my HA (another Arduino, Mega). This means: in case of a Mega, only 4 interrupts are left.

Anyone has some ideas or tips? Is it even possible with one Arduino?

4  Topics / Home Automation and Networked Objects / Re: Connecting arduino to existing house wiring on: April 18, 2014, 04:34:37 am
This schematic is not made by me, but by someone designing harddisk controllers (a professional).
The idea is:
D2 is for negative spikes.
R2 and R3 are for power absorbing of high energy spikes.
R4 is for pull down.
R1 is 'opening' D3. Zeners are very slow, they could be damaged by a high energy spike.
D1 is for positive spikes, this spike is grounded via D3. Because of the slowness of D3, C1 is for capturing the first 'start of the spike'.

Maybe it's a bit overdone for home-purposes, but I've had some troubles with spikes conducted by switching power supplies and TL lighting, which was all gone with this solution.
With this, the voltage to the Arduino input will never be over 5V, although I don't know what the maximum input voltage is?
Otherwise it might be indeed an idea for a higher D3 for less power consumption.
5  Topics / Home Automation and Networked Objects / Re: Connecting arduino to existing house wiring on: April 17, 2014, 01:12:42 pm
I know Polyglot doesn't like the idea, but depending on where you live, wiring is not a big issue.
If we forget all the legal stuff, this is my setup (all credits for the schematic to Vincent Himpe, alias free_electron):

This is working for quite a while at my home, no failure at all.
All with ordinary wires, though I admit that shielded wires would be preferrable. Total current consumption with closed switch is aprox. 2 mA.
6  Topics / Home Automation and Networked Objects / Re: Connecting arduino to existing house wiring on: April 15, 2014, 01:58:32 pm
Unlicensed people connecting unapproved devices to fixed wiring is illegal in most jurisdictions and will invalidate your house insurance

Maybe you're right, but isn't this whole forum all about connecting unapproved devices to our home installation?
Connecting 5 Volts to an ordinary switch will not cause any fire, but noise may ruin your Arduino indeed.
To let your Arduino switch any light, you'll need automatically opto-isolation like relay or solid state relay.
7  Topics / Home Automation and Networked Objects / Re: Connecting arduino to existing house wiring on: April 14, 2014, 12:29:20 pm
The thickness is not the problem (although I think it's 1,5 or 2,5 mm2 instead of 4).
From my own experience I know picking up spikes is the major problem, spikes will arbitrary switch your lights on and off  smiley-eek
Two ways to handle spikes:
1 (best): use shielded wires.
2: use a spike killer.

A spike killer works fine for me (and my Arduino, who's still working after 2 years of home automation).

There's a third option: a long delay (e.g. 300msec) to avoid switching by spikes, but it has two disadvantages
1- you'll notice the delay.
2- there still is a possibility that a nasty spike will kill your Arduino.
8  Using Arduino / General Electronics / Re: I adapted a scematic, PROBLEM: I'm a noob--> CHECK? on: April 13, 2014, 01:45:50 pm
It's ok, always use common ground with different voltages.
9  Topics / Home Automation and Networked Objects / Re: Arduino + Raspberry Pi Thermostat and Zone Control -- Need Guidance on: April 18, 2013, 12:47:37 pm
6) What does it take to build a thermostat circuit?

For my project, in each room (zone) I installed a Honeywell Round on/off thermostat (T87G1006)
It's a power stealing thermostat, so no batteries needed.
I've made a small circuit to give a signal to the input port of arduino.

The benefit of this, is that I don't necesserally need a tablet to control the heating system, also I see the actual temperature on the thermostat.
The best way for mounting a thermostat/sensor: ca. 1.5 meters above floor, watch out for draught and lightbulbs (warmth).
10  Topics / Home Automation and Networked Objects / Re: DS18B20 and MOSFET on: April 14, 2013, 01:59:07 pm
You can't power the 1-wire bus with a mosfet, you need a pull-up resistor. Why shouldn't you use a pull-up resistor?
The data line of 1-wire pulls the (5V) line low, to prevent short-circuit you'll need a resistor.
See also
11  Topics / Home Automation and Networked Objects / Re: How to connect a finger probe sensor (SPO2 sensor)to an arduino board? on: March 21, 2013, 02:06:50 pm
For question 1: just use the Rx and Tx pins, they are the UART pins. It's all serial, so use Serial.print or read for communication. You have to set the baudrate to a known speed, e.g 9600.

BUT: are you sure it's serial communication? I think they just use the DB9 connector because it has 9 pins, not for serial communication.
12  Topics / Home Automation and Networked Objects / Re: Why's SD -> Ethernet Card -> Webbrowser so slow? on: March 17, 2013, 02:48:52 pm
While quite busy working on my Arduino home automation project, forgot to look at this forum.
And see what happened: lots of discussion and good tips, thanks everbody, I'm gonna study all comments!
13  Topics / Home Automation and Networked Objects / Re: Home automation project on: January 22, 2013, 01:38:29 pm
Wat's exactly the problem?
I assume you've connected the relays to an output pin of your webserver (which you control by a webbrowser).
Now you've connected a pushbutton to your webserver, also to control the relays.
In that case you still know the position of the relay (i.e. the status of the output pin).
14  Topics / Home Automation and Networked Objects / Re: simple home control system on: January 22, 2013, 11:26:04 am
what happens: If switch 15 == LOW, you jump to afsluiten.
millis - starttijd is not greater then 5000, so nothing happens and void loop starts again.

Then again, starttijd = millis, we jump to afsluiten and again (and never will...) millis - starttijd is not greater then 5000.

So make sure you only update starttijd once.
15  Topics / Home Automation and Networked Objects / Re: How to control LED using Arduino as a webclient? on: January 06, 2013, 03:59:24 pm
Maybe this will help?
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