Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

4 pole relay to reverse polarity in steps

Status
Not open for further replies.
Nate,
In my schematics, the relay coil will be unpowered during the OPENING phase(1) and remain unpowered through the OPEN phase(2). It will be powered during the CLOSING phase(3) and the CLOSED phase(4).

When you find a possible dawn/dusk detector post it. Happy hunting.

Ken
 
Hi Ken,
whats the point of the diode across the relay coil?

Nate,
 
Last edited:
It's called a "freewheeling" or "flyback" diode. It's there the protect the transistor. When you turn off a relay it produces a large, opposite-polarity voltage across the coil terminals. The diode shorts it out so it doesn't damage the transistor. It's not always necessary, but is a "best practices" design. For very small relays the 1N4148 is OK. For bigger relays, use a 1N400X series diode.

Ken
 
Last edited:
Ken,

As the circuit looks now I'm going to have to supply current to the coil the whole time in the close phase (I'm not concerned about the power consumption) I'm worried about the noise the relay might produce (I can live with noise for the breif time that the motor is working but if it has to stay powered all night... well :(

you think we can make this work with a DPDT "latching" relay? So that power (if I find a way to do it)only has to be applied momentarily to the coil.

Nate,
 
Is this speculation or are you experiencing noise from a relay? A normal DC relay should not make any sound, other than the click as it switches on and off. If it's buzzing when powered, there's probably a problem with the power supply.

Ken
 
I think It's actualy going to work!!! :) :D

can you just explain to me what this part of the circuit is?
I understand is has to do with my light sensor but can you please give me a better understanding of what this exact part(s) does?



see attached,

thanks,

Nate,
 

Attachments

  • motor relayed circuit.gif
    motor relayed circuit.gif
    11.1 KB · Views: 235
Last edited:
The resistor and transistor are used as an amplifier to help the light sensor circuit drive the relay. A positive voltaged applied to the left end of the resistor (R1) will turn the transistor on, which turns the relay on. Zero volts on the resistor holds the transistor off, which holds the relay off.

If you look at that part of my circuit, and the right part of the circuit in: https://www.electro-tech-online.com/attachments/lightsensor-png.6712/ you will see that they are the same. (Ignoring the differences in our graphics). The added diode, D2, in that circuit is just more protection for the transistor. I don't think it's necessary.

Ken
 
Last edited:
thanks Ken,

say I wanted to override the circuit(I want to close the shades once during the day (I can just throw a switch in there) but... then I would have to flip the switch back for the shade to go back to it routine. hmmm... :(
 
The manual bypass would be a wise idea. For an automatic reset...may be a way of resetting back to 'light control' the next time the light sensor switches?
Options:
microcontroller...digital logic...relays/resistors/capacitors

Ken
 
Yes Ken, good point.

but before I started this project I decided that I wanted to try keeping the whole thing mechanical (ruling out the microcontroller) :(
I want to try building it all Logicaly.

Nate,
 
Nate,
In my schematics, the relay coil will be unpowered during the OPENING phase(1) and remain unpowered through the OPEN phase(2). It will be powered during the CLOSING phase(3) and the CLOSED phase(4).

When you find a possible dawn/dusk detector post it. Happy hunting.

Ken

Ken,

don't you think I should wire it so that the relay receives power in the opening phase and remains powered in the open phase and unpowered in the closed phase?
because if I use a LDR then it will allow power to pass only during the day when it's light out (when light shines onto the LDR its resistance falls)

Nate,
 
Just had another look at the the photo sensor circuit. Its relay is turned on when the LDR is lit. The input on my motor control was drawn before I saw that circuit. Just swap the "OPEN/"CLOSE" labels on the input signal and relay contacts, and "OP-LIM"/"CL-LIM" labels on the limit switches in my schematic. Of course the polarity to the motor will depend on the direction of rotation needed in your mechanical setup.

Ken
 
do you think I need a darlington setup? or is on transistor going to be enough?

Nate,
 
It depends on what relay you are going to use. Have you selected that?

Ken.
 
hi there Ken,

ok so here's what I have so far,

this is the relay I have in mind.
Digi-Key - Z1636-ND (Omron Electronics Inc-ECB Div - G2R-2-S DC12(S))

I found these motors that have a gearbox already build in, they all turn a reasonable speed for the shades.
DC Motor: High Torque Mini 12V DC Gear Motor, 50 rpm for Hobby Projects - MT-050
DC Motor: High Torque Mini DC Gear Motor 3-12V, 25 rpm for Hobby / Robots - MT-WSM500
**broken link removed**
Gear Motor 3: Right Angle Shaft

2 of these Limit switches
SPDT Switch with 3/4" Roller Lever - RadioShack.com

I haven't really found a LDR yet but for temporary experimentel porposes I have a honeywell 120320 laying aroud(it's a flame sensor for a boiler but works much in the same way as a regular LDR, I tested it with a multimeter)

I bought the 2N3904 transistor that you recommended and I also bought a TIP120 Darlington transistor.

I bought 1N4003, 1N4005(rectifier diode), and 1N4148 diodes.

I guess I'll have to use 12v to power the whole thing.

ok, so what do you think? will all these components fit in with each other? because on a simulation program that I tried the curcuit on, the diode were giving me problems.

what's your say(opinion) in the whole thing?

Nate,

edit: also if you think I'm using the wrong part(s), please don't hesitate to let me know (I won't get offended (smile) )
 
Last edited:
Nate

Looks like the relay, a 2N3904, 1N4003's, and the Microswitches should work. One of those motors should do the job...but it depends how much torque it will be required to open and close the shade.

Since you mentioned Radio Shack, they have a Cds photocell variety pack. One of these should work. CdS Photoresistors (5-Pack) - RadioShack.com

What problem occurred with the diode?

Ken
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top