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1  Using Arduino / General Electronics / Re: comms using a current loop on: January 12, 2014, 02:50:22 pm
Yeh, I'll be the 'poller', the other end likely has the resistors and such already in  place.
To be the client, it sounds like all I need to do is add a transformer, I'm not yet sure if it's AC or DC, and what potential.

To find that out, I suppose I need to know the resistance on the other end...
Then, to talk to it, the opto isolator should be all that is needed?
2  Using Arduino / General Electronics / comms using a current loop on: January 12, 2014, 03:06:50 am
I've played with RS485 and TTL comms before.
I've come across this interesting page, and I realise at the base of it all, It'll be digitalWrite type bit banging to make this type of comms happen.

What I'm unclear on is how I interface to the current loop as the master?

I think opto isolaters will be a must, but I'm not sure what goes between the opto isolater and the + and - cabling from the current loop..?
3  Using Arduino / General Electronics / Re: Through Hole PCB - Traces? on: December 24, 2013, 09:56:55 pm
Ahhh, I was aiming for terminals - I suppose I still can, just take the lead of the MOSFET to the terminals..

Thanks for the ideas! I'll some thick insulated copper wire to go to the terminals, and solder to the board for mechanical support.
4  Using Arduino / General Electronics / Through Hole PCB - Traces? on: December 24, 2013, 03:43:29 am
I've got a through hole PCB (one of them that has millions of prepunched holes). I've used them before with typical jumper wire to move off the breadboard.

I've got a problem - MOSFET on one of these PCBs, they typically require more current than a bit of CAT5 cable will accomodate.
Any thoughts?
5  Using Arduino / General Electronics / Re: MOSFET questions on: December 23, 2013, 10:19:51 pm
Define quick?
I'd still get a slow down in speed if I was switching them say fastest 400ms timebase (so 50% duty cycle = 200ms On period)?
6  Using Arduino / General Electronics / Re: MOSFET questions on: December 23, 2013, 03:16:37 am
It will be with PWM, so I've gone and got some heatsinks.
To solve the 10V issue, I plan to use some 2n3904 transistors to drive them on / off,  so it'll be 5V on to the base, which will have 12V at it's emitter and the gate of the MOSFET at it's collector..
7  Using Arduino / General Electronics / Re: MOSFET questions on: December 22, 2013, 11:07:30 pm

That's the MOSFET i'm looking at - 0.005 ohms.

The math I've applied is 10A x 0.005 = 0.05, this times by the amps is 0.5 W, so the MOSFET will dissipate 0.5W when switching 10A?
8  Using Arduino / General Electronics / Re: MOSFET questions on: December 16, 2013, 04:24:18 am
Let me check this is right..
8A x 14V is 112W
112W x 0.45 deg C/W Junction to Case is 50.4 deg C.
50.4 deg C + 30 deg expected ambient is 80.4 deg.

80.4 deg C is less than the datasheet Operating Junction Max Temp of 170 deg C.
It's Junction to Ambient is 62 deg  C/W.

No heatsink needed - or have I got it completely backwards?
9  Using Arduino / General Electronics / Re: MOSFET questions on: December 08, 2013, 07:08:55 am
A thermistor can't be connected to the MOSFET, now can it.. smiley
10  Using Arduino / General Electronics / Re: MOSFET questions on: December 08, 2013, 03:29:44 am
I'll probably stick relays in with it - MOSFET, and when the load is greatest, I'll use the relays.

When do MOSFETs produce the greatest heat ? I recall reading somewhere that when switching (i.e. not fully on), they get their hottest - is that right?
11  Using Arduino / General Electronics / MOSFET questions on: December 08, 2013, 02:49:38 am
I'm looking to take a signal (from a car ECU) to a MOSFET (it is PWM), then if the MOSFET fails (i.e. due to inadequate heatsinking, or else), that it fails in a closed state so that the output (Radiator Fans) stay on.

Can I sink the heat off the MOSFET to the car frame, given that it is also ground, or will that affect operation?
12  Using Arduino / General Electronics / Re: Transmit a signal over a wire far away. on: December 06, 2013, 05:55:18 am
Open air wireless is an option too...  there's some transmitters around - nrf come to mind.
13  Using Arduino / General Electronics / Re: current detector with led power on on: October 29, 2013, 02:48:26 am
How many turns is needed?
14  Using Arduino / General Electronics / Re: help with a relay on: August 17, 2013, 07:27:18 am
You can use those components to control a relay.
Now you need to determine how you'll use those components to control the relay - plenty of examples out there.
15  Using Arduino / General Electronics / Re: 1st Project for newb on: July 13, 2013, 07:31:20 am
Battery operation - I'd suggest looking into a few things (minor if you have solar backup):
- Regulator - switching regulators waste less power.
- Sleep mode - the application really should only drive that door twice a day, so the chip can go into low power mode ('sleep') for a majority of the time (let's not get into whether the duino is needed).
The application really just calls for two executions (morning and night). If it gets dark all of a sudden (rain, shadowing).. you don't want that door cycling down preventing entry.

Circuit protection wise,
over current on the motor doesn't seem to be protected (i.e. motor jammed stall current exceeds driver chip or cable ratings).
fuse the battery supply to the duino to the max expected during motor operation.
freewheel diode not present across the motor (when it turns after you turn off, high voltage is generated, so L298N could be subject to V > allowed.
check spec on datasheet and motor for current requirement.

Of them all the fuse is fairly important - overcurrent or a short (chickens can be fairly docile) will produce heat and may start a fire.
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