Attempting to design an automated car shade, need help with the circuitry.

Thread Starter

Shurrie

Joined Jun 19, 2020
5
Hello!

I am trying to design a car shade (the thing you put up in your windshield to block the sun) that is automatic with the press of a button. I have an idea of how it will work and the design, but I am struggling with the circuit.

Here is some background:
The automatic shade will be rolled and unrolled from inside of a casing at the bottom of the windshield with the use of a DC motor.
Don't worry about the logistics of how it will stay up/material/etc, that is not a problem.

Here is the requirements of the circuit:
-When a button/switch is pressed, the motor needs to unroll the shade so that it covers the windshield.
-The circuit needs to stop at a certain point (when the shade is fully unrolled).
-When a separate button is pressed, the motor needs to roll up the shade (turn the opposite direction).
-The circuit needs to stop at a certain point (when the shade is fully rolled up).

Here are my ideas:
- Use a small regular DC motor for the turning (with a potentiometer to regulate speed if needed)
- Use a DPDT switch in order to turn on the circuit and be able to change the direction of the motor( the switch settings would be CW, off, CCW)
- Use a 555 timer in monostable mode to control the amount of time the motor will turn (rather than using a sensor to stop the circuit when the shade reaches a certain point)

Here are my issues:
- If the DPDT switch as the trigger of the 555 timer, will i need two separate timers for the two separate directions the switch?
- I don't have a lot of experience using any of these parts, so I'm not sure how I would put the circuit together or if it would even work, a circuit diagram would probably help.
 

jpanhalt

Joined Jan 18, 2008
9,785
Here are my issues:
- If the DPDT switch as the trigger of the 555 timer, will i need two separate timers for the two separate directions the switch?
- I don't have a lot of experience using any of these parts, so I'm not sure how I would put the circuit together or if it would even work, a circuit diagram would probably help.
Since it is a learning project...

Issue #1: Do you expect the timing to be different in each direction? Why?
Do you think time is the best way to determine whether the shades are fully open or closed? What if a bug gets stuck and slows the movement down? If mechanically driving, I would use a mechanical measure, such as rotations or strokes, or a limit/beam break switch. All sorts of small neat devices are available for doing that. If it does get stuck, you will want some sort of safety or time-out switch so the motor is not kept in a stalled condition for very long.

Issue #2: It's your learning experience, but you seem to be asking for something you can just put together as a kit without defining what you really need. Designing a circuit is relatively simple. You need to define in more detail what you want the circuit to do.
 

LesJones

Joined Jan 8, 2017
2,671
I agree that the timing method will not be reliable. Here are a few suggestions. 1 - Add small gearbox on the drive roller that rotates about three quarters of a revolution for the full travel of the blind. Have two disks with notches in them so one operates a microswitch in the up position and the other operates a microswitch in the down position. 2 - Have notches or reflective markers on one edge of the blind to detect the up and down positions. 3 - generate a number of pulses for each revolution of the blind roller and use them to increment a counter in one direction and decrement a counter in the other direction. The counting would be done with a microcontroller and you would have setup function to teach it the count for the up position and for the down position. I have used this method for a window blind that has been working for several years. (I used a reflective opto sensor to generate the pulses.

Les.
 

jpanhalt

Joined Jan 18, 2008
9,785
:)

Do we know the blinds will move up and down and not horizontally -- maybe split in the middle? Perhaps they will be above the headliner and come down like garage doors? Slats or accordion like? Maybe the blinds won't move at all and will activate LCD-like?

So far the TS has only imaginary blinds and is stumped on whether he needs one or two 555's for timers.

Of course, we both neglected asking what will happen if it is night, raining, and the blinds suddenly activate at 60 mph. However, as an exercise, I am willing to ignore safety aspects until the inventor comes up with a practical mechanical design and needs help on the electronics.
 

Thread Starter

Shurrie

Joined Jun 19, 2020
5
Thank you for the suggestions, I suppose the car shade portion of the project is unimportant.
I think time is a good way to gauge how long the motor should turn because with a 555 timer you can change the time easily with capacitors and resistors.

As for the requirements of the circuit I suppose it would be:

Press a button, motor turns (slow/medium speed) for about 10 seconds then stops.
Press a different button and the motor turns the opposite direction for the same speed and time, then stops.

I guess I am just trying to learn/understand how the components would need to interact to work properly without using a microcomputer. I know I could program this pretty easily with a timer in arduino, but I've never worked with a 555 timer.
 

jpanhalt

Joined Jan 18, 2008
9,785
Thank you for the suggestions, I suppose the car shade portion of the project is unimportant.
That's in the title of your project. That usually means it is important.
I think time is a good way to gauge how long the motor should turn because with a 555 timer you can change the time easily with capacitors and resistors.
Thank you for ignoring my advice. Why do you think time is better?
As for the requirements of the circuit I suppose it would be:

Press a button, motor turns (slow/medium speed) for about 10 seconds then stops.
Press a different button and the motor turns the opposite direction for the same speed and time, then stops.
Very simple to do. What's your best effort?
I guess I am just trying to learn/understand how the components would need to interact to work properly without using a microcomputer. I know I could program this pretty easily with a timer in arduino, but I've never worked with a 555 timer.
You can use the arduino to do the same thing. So, why did you decide to use an inferior method of timing, namely a 555? Is this homework? Do you intentionally want a second-rate solution?
 

Thread Starter

Shurrie

Joined Jun 19, 2020
5
The project idea was just an idea, thus the unimportance. Now I am just trying to learn about the circuit components and how they would interact.

Your advice wasn't ignored, I just think within my range of capabilities I would be able to understand a timer more easily. I was also considering using some sort of motion sensor, and I wouldn't know where to start with the gear box idea or using mechanical measurements, though I'd be willing to try if the pieces are cheap and you can point me in the direction of some sort of tutorial.

My best effort is what I stated, using a DPDT button to control direction of the motor, using a timer to control time, and a DC motor for the turning. My problem is I don't know if the change in direction of the current would affect the timer, or how I would hook these things up together.

I don't have an Arduino readily available and they are more expensive than the pieces I have mentioned.
 

dl324

Joined Mar 30, 2015
11,000
Here are my issues:
- If the DPDT switch as the trigger of the 555 timer, will i need two separate timers for the two separate directions the switch?
- I don't have a lot of experience using any of these parts, so I'm not sure how I would put the circuit together or if it would even work, a circuit diagram would probably help.
Using limit switches or counting the number of revolutions of the motor would be more reliable than just timing the motors.

Limit switches would be a more robust solution because if the motor ever stopped before the limits had been reached, a timing or revolution counting circuit would have no way to recover from that condition automatically.
 

Thread Starter

Shurrie

Joined Jun 19, 2020
5
You're right!

I looked up limit switches and they are perfect. Sorry, I had never used them before.
I figured out the circuit, thanks guys.
 
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