help in relay board making

me and my team was looking for the possibility of making an 8-channel relay board that can handle 220volts household appliances that can be powered using this relay. my team is advised to create a relay board and not to use ready made product so that i look up in the internet and found this.. ithink theres a way of making this relay board..i also have the schematic diagram of this.. but there is the problem the value of components that will be use.. this is the relay board..

please help me with this. thanks!

Try a slightly different approach - use a shift register to control the coils.
TPIC6C595.
1N5819 diode across the coils.
1K resistor with the LEDs.
Wired like this, expand as needed, change to desired relay. SPST is all you need really if just turning power on/off to appliances.

CrossRoads:
Try a slightly different approach - use a shift register to control the coils.
TPIC6C595.
1N5819 diode across the coils.
1K resistor with the LEDs.
Wired like this, expand as needed, change to desired relay. SPST is all you need really if just turning power on/off to appliances.

uhm.. actually the relay will be connected to receptacles / power outlets in able to plugged appliances on it..

Well, I thought CrossRoads' answer was perfectly good. What problem are you seeing with it?

What is your deadline? I would expect for a school project that if you've been asked to make your own board then the entire project is building the board. If you are just using this as a component in a project, then don't mess around with trying to make one. There's a lot of issues with mains voltage that you really don't want to deal with unless that is the actual subject of the project.

Having only seen the provided photo of the top side of that board, I would say that it looks perfectly fine to use in a mains powered project. Just buy one already. Build it into a box (power strip) and show your adviser how careful you have been to keep the high-voltage side of the relays separate from the low-voltage Arduino wires. You need to build a "dam" of insulating material around the middle of the board so that any wire that comes loose can't cross over to the other side. That dam can be a piece of plastic cut from an icecream container that just fits over the relays. Or glob it up with hot glue or silicone sealant. That works too.

I posted a drawing yesterday, search "home automation", as way to connect wall outlet type connectors to the relays. Plug in your unmodified appliance (fan, light) into a normal looking socket, relay board behind the scenes takes care of make/break the hot line of the 120V.

This drawing.

Start with the requirements for the load the relays must switch, choose appropriate
relays and then check the datasheet for the voltage & current needed to operate
them. They you choose a transistor, base resistor and diode to switch the winding,
then consider the input (such as shift register, opto isolator, whatever). You also
need a power supply for the relay windings.

Don't use a silicone sealant unless its rated for electronic use.

What's missing in the picture you provided is optical isolation. Wouldn't this be an important feature to have when controlling mains powered equipment?

Another consideration might be if you would want to include any snubber circuitry on the relay contact side to reduce EMI/RFI and extend contact life.

Another consideration could be the proximity of your board to the MCU and logic circuitry. Would this be a remote board or designed as a shield?

If the number of available control outputs is a consideration, CrossRoads suggestion would alleviate that and allow for ease of expansion.

I'm curious as to what are the reasons to create a new board where an off the shelf product wouldn't work?

Optical isolation isn't needed. The relays provide the isolation. Does a wall switch provide optical isolation?

For example, here's a relay shield I made controlling 8 strings of Christmas LED lights

Opto-isolation might be a required feature - depends on the requirements of the OP, i.e. is this new board intended to be universal, is the power source derived from the same mains, what degree of isolation is required, etc.

https://arduino-info.wikispaces.com/RelayIsolation

EDIT: Opto isolation could be helpful for products used in an environment susceptible to lightning or in a noisy electrical environment.

CrossRoads:
I posted a drawing yesterday, search "home automation", as way to connect wall outlet type connectors to the relays. Plug in your unmodified appliance (fan, light) into a normal looking socket, relay board behind the scenes takes care of make/break the hot line of the 120V.

yes sir this is what will look like and ours must powered up 220v..

CrossRoads:
TPIC6C595.
1N5819 diode across the coils.

OK, you have me curious now.

Why do you always specify the diodes across the relay coil when the TPIC6C595 implements the clamps especially designed for this purpose (which also FWIW, speeds up the release time of the relays)?

I see no diode in the TPIC6B595 from the drain (anode) to a High Voltage supply pin (cathode). Perhaps you are thinking of the ULN2803.

You need to read the datasheet carefully.

Notably page 1 and the second (right-hand) diagram on page 3 which illustrates an active clamp utilising the output FET.

The ULN2803 functions differently; the TPIC6B595 design has a number of advantages, not the least of which is circuit simplicity.

I'm going to stick with the safe design and recommend the diode across the coil for spike dissipation.
The 6C595 has lower voltage protection.
For a nickel an output it's pretty inexpensive to be safe.

This thread is a bit scary....

If the idea is to use a relay board as part of a bigger project, it makes little sense to make a board when there are so many safer alteratives off the shelf.

If, otoh, the learning objective is to make a relay board, then I'd expect the OP to be further ahead in electrical know-how than this:

i think theres a way of making this relay board..i also have the schematic diagram of this.. but there is the problem the value of components that will be use..

.... before tackling a mains voltage project.

I'm with MorganS on this one, for sure.

my team is advised to create a relay board and not to use ready made product so that i look up in the internet and found this..

School project?

JimboZA:
This thread is a bit scary....

I agree.

Hi,

Why do you always specify the diodes across the relay coil when the TPIC6C595 implements the clamps especially designed for this purpose (which also FWIW, speeds up the release time of the relays)?

He must have Irish blood flowing in his veins, To Be Sure, To Be Sure.

Tom.. :slight_smile:

TomGeorge:
He must have Irish blood flowing in his veins, To Be Sure, To Be Sure.

Well, I give up. :astonished: