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Old 19th June 2013, 14:35   #1
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Default Calling electronic experts: DIY GSM-controlled module for home appliances

Basic project is to control a home appliance through GSM.

For that, i have bought the following items
1. Arduino Uno micro controller
2. Sim 900 GSM module
3. Buffer ULN 2803 A
4. Relay 12v
5. Misc items (resistors etc)

Now the problem here is, Relay is rated 12 Volts and Arduino micro controller is 5 volts.
Electronic shop fella mislead me into buy this combo instead of buying a same specs 5volt relay.
As per him, adding a ULN 2803A buffer would resolve the issue but i'm unable to find data sheet online to freeze the connecting points between buffer and relay.

Also, the relay has no marking, so not sure what the 5 points denotes (+ve/ -ve/ common/ NO/ NC)
So, would need advise on how to connect the buffer to relay.

Calling all electronic experts here to bail me out of this.

Frankly, I'm a novice in electronics, just doing this DIY for fun. So, pardon me if some queries sound stupid.

Basic circuit
Calling electronic experts: DIY GSM-controlled module for home appliances-dsc_0034.jpg

Arduino micro controller
Calling electronic experts: DIY GSM-controlled module for home appliances-dsc_0030.jpg

IC buffer ULN 2803
Calling electronic experts: DIY GSM-controlled module for home appliances-dsc_0032.jpg

Relay 12v
Calling electronic experts: DIY GSM-controlled module for home appliances-dsc_0031.jpg

GSM module
Calling electronic experts: DIY GSM-controlled module for home appliances-dsc_0029.jpg
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Old 25th August 2013, 14:03   #2
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Default Re: Calling electronic experts: DIY GSM-controlled module for home appliances

@kpzen What happened to the Home automation Project ?

Did you sort out the relay connection to the buffer chip ? I am curious as I am planning to do some automation using Arduino and Wifi module.
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Old 25th August 2013, 17:57   #3
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Default Re: Calling electronic experts: DIY GSM-controlled module for home appliances

Why not wait for the Belkin WeMo to arrive here instead ?
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Old 25th August 2013, 18:05   #4
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Default Re: Calling electronic experts: DIY GSM-controlled module for home appliances

@kpzen, use the ULN 2803 A buffer (only 1 is needed out of the 8, maybe 2 if the coil current of the relay if coil current is >500mA - unlikely) to drive the coil of the DUMAG relay. From what you have described (+ve/ -ve/ common/ NO/ NC), the relay connections are:

1. +ive: one side of the relay coil. The 12V +ive line should be connected to this point, as also the COM point of the Buffer IC (it brings a reverse connected flyback diode in the chip into play to dissipate the negative surge of coil current switching)

2. -ive: the other side of the coil. This would be connected to the Output pin of the buffer (Pin 1C etc.). The 5V and 12V grounds have to be connected together

3. Common is the Common point of the NO/NC contact (this is not associated with the Coil). In the inactive condition of the relay (no current flowing through coil), this makes contact with the NC side

4. NO contact: Normally Open contact. The coil pulls the armature when current flows through it, connecting the Common to the NO contact; otherwise it is isolated

5. NC contact: Normally Closed contact. This is connected to Common when no current flows through relay coil, and is 'opened' or isolated when coil pulls armature

Coil +ive Common
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Coil -ive NO NC

For your application, you will need to connect the Common to the Supply side (which I assume is 230V 1ph 50Hz AC), and the NO contact should be connected to the Phase line of the socket into which the appliance will be connected. A high at the Buffer Input will cause current to flow through the Relay Coil, and hence the Appliance will get power. You only have to apply 5V to the input of the Buffer (Pin 1B etc.) through which ever Port pin you connect (i.e. make that pin go high by writing 1 to it).
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Old 16th September 2013, 20:38   #5
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Default Re: Calling electronic experts: DIY GSM-controlled module for home appliances

Reviving this thread as I require some info about working with arduino. I am designing a circuit used for controlling lights automatically, or rather trying to build a circuit to switch on and off the headlight and also a logic to switch beams.

Let me come to the issue in specific. I would like to switch ON the setup using the Parking light signal ie available at 14.5V max. That will act as an 'Auto' Position and the MC will start up. Also suppose a signal comes from either high beam or low beam, the circuit will go to manual mode and will not function. For this, I need three inputs. One from parking lamp, HB and LB.

This will be my first circuit based on Arduino and hence I need to get my basics right. Hence what ever I will say will be based on what knowledge I have gained so far.
1. I understand that my Arduino Uno needs a 5v as an input logic high. For this, is it fine if I use a 7805 regulator, then directly supply the 5v output to the Digital input, is it fine? Will it burn the board? Else what is the workaround? Do I need a current limiting resistor and a capacitor? Will analog IN be a better idea, given that I have them unused?

2. In what way can I power the board using the source(14.5v) I have with me? I have the following options in mind:
  • Supply 14.5v at the DC in jack. I hope this wont cause problems, or
  • Use the 5v regulator(7805) and find a port that takes 5V into the board(No idea about this)
  • Get a 9v/12v regulator and get back to using the DC jack.

Do let me know how I should go about these two issues. Any comments, suggestions and corrections are welcome!
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