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31  Topics / Device Hacking / Re: arduino air conditioner on: May 12, 2013, 07:37:03 am
IR to see what is being sent to the A/C from the remote, and reproduce to get desired setpoint.
Plenty of IR examples.
The hard part is decoding the data.
32  Using Arduino / General Electronics / Re: noise on: May 09, 2013, 05:12:31 am
What do you mean analog pin decoupled?
Sensor cable isn't shielded, just security system cable.

The ground point is all soldered back to a single ground point.

I think from what you are saying, I should have multiple ground paths to the single point - i.e. the ground reference for analog input should be direct to the ground point? and independant to the chip's supply ground.

It is just thermistors, but the graph I've been getting is bouncing like crazy when pump is running and stable without.
33  Using Arduino / General Electronics / noise on: May 09, 2013, 03:59:23 am
I've got an arduino that I built as a standalone, and I'm wondering why is it when a pump status comes on, I get a lot of noise on the temperature sensors.
When the pump status point is off, there's no problem?

The pump status input to me is soldered to a PIC pin which switches a relay on / off.
The temperature sensors are simple thermistor, resistor divider to input.
The ground path is common all ground requirements are soldered back to the one location.
34  Using Arduino / General Electronics / Re: Digital Input from an LED on: April 24, 2013, 05:02:46 pm
I would use an analog input, but as the arduino only has 6 of them, I wish to use them for other purposes.
The intent is to pick it up as a digital signal, so I'm after a method of doing that.

What I don't yet know is whether direct to a transistor base pin is good enough or so

Cutting off the LED isn't ideal.
I've found a better output from the PIC pin which looks like it drives when needed.
35  Using Arduino / General Electronics / Re: Digital Input from an LED on: April 24, 2013, 08:29:20 am
Same signal - it was 0.5V off, and 1V on.
36  Using Arduino / General Electronics / Digital Input from an LED on: April 24, 2013, 08:09:17 am
Interfacing to another PCB, I'm looking to pick up that a pump is being driven on.
The back of the PCB has 4 LEDs commoned up on one side (I assume the ground side - anode of the 4 LEDs)
On the other side of the LEDs, after a resistor is where I've picked up what should be a digital signal - high when the LED is being driven on, and low when LED is off.

Metering this, I was expecting (perhaps incorrectly) that the voltage would be 5v (the LED would be driven from the onboard PIC).
What I got was 0.5v when the LED was off, and 1v when the LED was on.
No problem, still a usable method of determining it.

My question based on the above is- I want to wire that into a digital input. So for it to read 'high', I think I need a transistor. If I use an NPN transistor from 5V to the digital Input, and feed it's base direct from the wire described above, will I get the desired behaviour?
37  Using Arduino / General Electronics / Re: Switching load between two sources. on: April 10, 2013, 04:11:05 am
I think it's a single phase in from the street.

One is just a controlled load.
I realise I posted this on a microcontroller forum, but I'm not fussed with manually switching it.
The idea is that the element in the hot water heater may get power directly when we wish, else it's controlled by the utility controlled load signal.

What I am missing is the name of such a switch (i.e. 3 terminals, load, source 1, source 2).
38  Using Arduino / General Electronics / Switching load between two sources. on: April 09, 2013, 07:53:33 am
I need a mains switch that can switch a load between two input sources.

Any thoughts?
I'm thinking something like the on / off / auto switch, but it only needs two positions (off peak, normal), and allow for the load to be switched between either of the two.
It'll want to be a 32A 240V rating (or thereabouts).
39  Using Arduino / General Electronics / Re: Thermocouple calibration on: April 09, 2013, 05:54:18 am
If those temperatures are in celcius, that sounds awfully close (and past) manufacturers design maximums.

Electronics derate above design temperatures.
40  Using Arduino / General Electronics / Re: Circuit which switches depending on power on: March 29, 2013, 11:37:34 pm
What's the switching time of such a circuit?
It sounds good..
41  Using Arduino / General Electronics / Re: 12v to 5v - Voltage divider issues on: March 28, 2013, 05:14:53 pm
I'm trying to consider why one wouldn't use an opamp buffer in this design?
It makes sense to me - accurate readings, no load on source circuit.
42  Using Arduino / General Electronics / Re: Force a sealed device to restart - Ideas? on: March 27, 2013, 02:51:43 am
Just thinking of the obvious - remove the power (Battery..)..?
43  Using Arduino / General Electronics / Re: A question about Arduino VIN on: March 26, 2013, 04:13:27 am
Where you have VIN, replace it with VCC, and VCC should be below 5V.

On the arduino board, VIN is before the regulator - so the 7805 regulator has an IN, GND, OUT - Out is always 5V, IN is "Vin".
44  Using Arduino / General Electronics / Re: Electric Circuit - Power Supply Issue on: March 22, 2013, 04:33:49 pm
Is the 12V supply a switchmode supply?
45  Using Arduino / Motors, Mechanics, and Power / Re: MOSFET for DC motors on: January 22, 2013, 07:28:08 am
Yeh, got the diodes (actually planned on soldering them to the relay bases originally).

With regard to heat sinks (I've calculated a probable 2W worst case to dissipate, I'm going with safe and adding them).
Thermal resistance is a measurement such as 8oC/W

2W gives me 136oC at 25 ambient to dissipate. It'll be higher than 25 ambient, so I need to lose around 110oC (if I work on 160oC and I want 50oC maintained, potentially higher)..
Would I not want a heatsink with a higher thermal resistance, such as 40oC/W ? I'm not sure why I'd want one lower (i.e. 8oC/W) but all my reading says to pick one with a 'lower thermal resistance'.
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