Motor reversal for blind with upper and lower cut off switches

[dj_barber]

Hi, I've given some thought to the idea of creating some automatic blinds, and with some electronics background have come up with a rough idea of parts needed but would like to ask for advice from the pros, if i may!

So, the circuit is to run a 12v DC motor (reversed polarity for reversed direction), with:

One main on/off SPST for the whole system.
Two momentary switches to operate system "Open Blinds", "Close Blinds".
Micro/momentary to be held by blinds when at an upper limit ("blinds are open")
Micro/momentary to be held by blinds when at a lower limit ("blinds are closed").


I had guessed a DPDT Latching relay would be the best idea, or a somewhat more complex setup with thyristors governing the latching. Can anyone offer any advice please? Oh, and yes i do have some eggs you can suck for the reversed motor polarity statement above!

Many thanks, Daniel


Oh, and yes i do have some eggs you can suck for the reversed motor polarity statement above! Thanks guys, your help will be greatly appreciated.

 

[strantor]

baleeted

 

[ChrisP58]

**broken link removed**

Strantor, you have a dead short when you press either of your two buttons through the NC contacts of the relays.

You need to insert a diode in each side between the PB/coil node and the limit switch/motor node. Cathode towards the limit switch.

 

[strantor]

damn, I guess I didn't baleet that fast enough

 

[strantor]

View attachment 64920

 

[dj_barber]

Wow thank you for the fast replies! Are those SPDT relays latching or just regular? Also the "up" and "down" buttons look to be SPST in your diagram, or are they PTM? D

 

[strantor]

regular relays, spst pushbuttons

 

[dj_barber]

I'm struggling to simulate this from your drawings Strantor, so it may be my interpretation skills, can i double check that you intended the following:

The higher switches labelled "up" and "down" are SPST momentary microswitches which are closed and held when the blind is in that position, and are released as soon as the blind moves from that position.

The lower switches labelled Up and Down are SPST momentary switches which are pressed and released by the operator to fully rise, or fully lower the blinds (until microswitches are closed by blind)


It appears that the switch labels are the wrong way around, and possibly need to be held for the motor to continue to run until a limit switch is hit? As i mentionned i have had some experience, but by the sounds of it no where near as much as you so i cannot thank you enough for taking the time to help with this! I am learning as i go along, and this is a learning curve for me! With every project i start with a drawing, simulate it with Yenka then go on to make it on stripboard or proto on breadboard. Is there any reason that the circuit you draw above would work in proto but not in simulation?

Many thanks
Dan

...no really, i cannot stress enough how grateful i am for your help!

 

[strantor]

The higher switches labelled "up" and "down" are SPST momentary microswitches which are closed and held when the blind is in that position, and are released as soon as the blind moves from that position.

correct. I would call them "limit switches" but I suppose "microswitch" is just as correct. They are Normally Closed (NC) and are opened when the blinds reach that position.

I've used yenka for about 5 min before I trashed it, so I wouldn't be able to explain anything regarding the program or simulation, but I'll give you a rundown how the circuit should work:
Initial conditions:
1. toggle switch is on
2. Blinds are all the down position, resulting in:
a. "down" limit switch is open.
b. both relays are inactive
3. no buttons are being pushed
The blinds will stay at rest in the down position indefinately, with no power being drawn by the circuit (negating the need for the toggle switch, unless you have other resons for it to be there)

You press the Down button:
1. nothing happens because the "down" limit switch is open. The only other path for current is through the diode which is in parallel with the limit switch, but that diode is reverse biased so no current flows.

You press the Up button:
(description provided in conventional flow)
1. incoming +12V power goes through coil of the relay on the right, and through the Up button, to ground. This actuates the relay.
2. Since the relay is now actuated, it's COM terminal is now connected to the NO terminal, thereby giving its own coil a new path to ground. So you can release the button and the relay will stay energized
3. The motor also has a path to ground now the relay is energized. Incoming power flows from the NC terminal of the Down relay to the COM terminal of the down relay, through the diode (forward biased now) which is in parallel with the "down" limit switch, through the motor, through the "Up" limit switch, from the COM terminal of the Up relay to the NO contact of the Up relay, to ground.
4. The relay coil and the motor share the same ground connection point, which is upstream of the limit switch. So when the blinds reach the up position and the "Up" limit switch is opened, the relay will switch off, along with the motor
5. You are now back to initial conditions, drawing no power.

 

[dj_barber]

Awesome, thank you Strantor! I have managed to get the simulation working, so will crack on and get it on a stripboard and in an enclosure! Will keep you posted! Many thanks, once again! D