I am working on a project to put electronic locks on "Jack and Jill" bathroom doors. I am building this project in blocks and my first block is the lock/unlock button (switch). While some blocks will likely require a microprocessor, I would like to built the button with discrete components.

I have chosen an RGB LED momentary button (similar to arcade type buttons) and need help making it latching and being red in one state and green in the other. I love Wendy's 555 latching design http://forum.allaboutcircuits.com/threads/submission-555-bistable-multivibrator.40717/, but I have been unable to get it to work with an RGB LED. I believe it is because it only has one cathode while her design uses two separate LEDs and thus two cathodes.

My question: Is it possible to modify Wendy's design to work with an RGB LED, if not, can someone recommend an alternative latching circuit?

Thanks in advance

 

So your RGB led has 3 Cathodes and one Anode., then you need to use three 555 latches or flipflops.

 

Sorry I meant cathode not anode. I have edited my original post to prevent further confusion.

 

If you could hand sketch a schematic showing what you are trying to do, take a picture, and post it I could be more help. Right now I can only guess how you are approaching this.

 

Thanks in advance, hopefully this state diagram will properly explain my intent.

 

Try this...

 

This sounds like a toggle flipflop with a power-on reset.

a. As long as power is on, pressing the button (only one button?) multiple times causes the lock to lock, unlock, lock, unlock...

b. When power is lost the lock goes to the unlock state.

c. When power is reapplied the lock remains in the unlock state until the button is pressed.

Correct?

If so, this can be done with a couple of transistors, or a logic chip. Depending on the power requirements of the electric strike, a 2-transistor ff might be able to drive it directly. The chip would need a drive transistor or triac. What is the electric lock power?

Gopher beat me by seconds... But, no power-on reset.

ak

 

Depending on current requirements for the actuator on the door you can also use a second 555 as an inverter (in other words, a 556, a dual 555).

You can also use on 470 for both LEDs instead of two by putting it on the cathode.

Power ups are relatively easy, but you need to define what the circuit is driving (solenoid currents).

This circuit will require 6V for stable operation, given the 555 3.8V output when powered by 5V. A CMOS 555 can do it, but then what does the solenoid need for current?

 

Here is a first pass. I've never been a big fan of the CD4013 flipflop, so U1A and U1B form a toggle flipflop with a defined power-on state. Because I get reset timing and switch debouncing out of the same capacitor, the left side of the circuit takes one fewer part than a 4013 design. The circuit is set up for +12 V to the chip and +12 V to the strike. However, the circuit and strike voltages do not have to be equal. For example, the circuit can run on 5 V and drive a 24 V strike. Depending on what parts you have, the strike can be driven with a bipolar transistor, or a power MOSFET. Also, the chip can be replaced with sections of a 40106 hex inverter. There are lotsa variations and possibilities.

EDIT: Corrected schematic.

ak

 

Thanks, you all. Will breadboard now.

AnalogKid,
abc are all correct. I have yet to select the locking mechanism (either electromagnet or solenoid based bolt), but it is likely going to be a high current DC device so I expect I will have to trigger it via mosfet or relay.

Thanks again,

 

All,
Got it working using the 555 solution, since I already had Wendy's design on my breadboard, I kept the 10K resistors and increased the resistor value at the transistor base. Attached is a picture of my circuit in spice. I could not figure out how to get the switch model to push twice, so I only get the Red LED to light in the simulation.

AnalogKid,
I have a bunch of NAND gates, but no 4093s, which I assume are needed to deal with switch bounce, so I didn't get to try your model, I ordered some, so I will try it later this week.

FYI, have a couple of new requirements:
1) I have door sensors (magnetic NO that are connected to my alarm system) on each door and would like the button not to change state unless both doors are closed. My plan is to add a NPN between the switch and the trigger - its base will only receive current when both doors are closed.
2) When both doors are closed and the button is pushed, I want the state of the other button to change as well, I think that just requires that I connect the two triggers together.

If this doesn't work I will be back!

Thanks again for all the help, I love this site!