Incoporating NO 5Vcc Leaf switch into 2x555 toggle/bistable circuit

Discussion in 'The Projects Forum' started by bigsanta11, Sep 25, 2010.

  1. bigsanta11

    Thread Starter Member

    Feb 6, 2008
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    Hello ,New member here,from the UK and i'm struggling with a problem .

    What i plan on doing is using the circuit to switch modes on a device ,3 modes in total.the device is supplying all power needs 5Vcc (It also has a 9VCC supply if need ,but it isn't)The first two modes are controlled only by the first ne555n.

    [​IMG]

    Mode 1 is activated when it receives a logic high (3 to 5 Vcc) and is kept at logic high,making mode 2 deactivated.
    Mode 2 is activated when it receives a logic low and is kept at logic low.making mode 1 deactivated,Both can be toggled while the device is running .

    Mode 3 is using the first 555's output to control the second 555's bistable output and keep it locked to a logic level after one of two events that happen on the device at exactly powering on the device,or about a second after the device is switched on.

    The first two LEDs will be replaced with a bi or tri colour LED,to indicate which mode (1 or 2)is activated ,LED 2 (indicating mode 3)on the diagram may not be part of the final product because of how mode 3 works.

    Mode 3 itself has two states,which are activated very awkwardly .e.g

    When the device is powered on and in a low state (which is how the second 555 starts up with the help of a POR ),the device selects a mode to use and keeps this mode until power is switched off,but it then needs a permanent high state about a second after to operate as normal .
    But to get this other mode (mode 4 in reality),the device is powered on and it gets a high state at the same time and is left in this high state to operate (hence the bistable).

    So trying to have a LED colour linked to what mode (3/4 )is on, won't work easily ,so i'll probably remove it.Mode 1/2 is easy enough though and that's problem one of two.


    The second problem is my main problem.

    It's the switch which is to activate the modes.I'm using a momentary push button while the circuit is on my breadboard,but i want to use the momentary switch on the device and it's an old type,i think it's called a leaf switch,two long strips of metal which are apart ,then pressed together to activate it.

    In it's NO state ,one side is connected to 5Vcc and when closed it is connected to 0Vss and sends this signal to an IC to reset the device.

    So far i haven't been able to work out how i can use this leaf switch in place of the one on my breadboard.Only by cutting the leaf switche's 0Vss trace to the device's IC and using the Vss from the output of the 555 as a reset signal works thus far,but i'd prefer to not cut the trace ,just incorporate the leaf switch somehow.

    Or i could just keep the two 555s seperate ,and use one with each leaf switch ,as the device has two leaf switches ,one is the reset and the other is a pause button which has a 4k7 pullup resistor .If i use this method i would like to try and have the reset button activate the first 555 when this leaf switch is held closed for one or two seconds,but reset would work as normal,immediately .

    I also have a few SN74HC74 ICs if those are usable?

    Also ,are there any improvements that could be made to my diagram,all help and advice is gratefully welcome.


    This is a link to a schematic for the device i'm using .IC 315-5216 is connected to the reset switch and IC 315-5124 shows how the pause button is connected.

    http://emudocs.org/Master System/master.gif
     
    Last edited: Sep 25, 2010
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It's been a long day for me, and I'm having a lot of trouble focusing.

    You seem to want a flip flop from the switch if I understand you correctly. What is the second 555 do? A monostable triggering off the 1st 555 when it goes low? If this is the case you forgot the isolation cap/resistor.

    555 Monostable

    Here is a super simple flip flop using one 555 I came up with a while ago...

    Submission: 555 Bistable Multivibrator

    I have a series of other 555 projects you might be able to lift from...

    The 555 Projects
     
  3. bigsanta11

    Thread Starter Member

    Feb 6, 2008
    14
    0
    Thanks ,i'll have a look at those ,but it's really just about how would i go about connecting the device's leaf switch in place of the temporary breadboard switch (between C1 and R1 and R2) ,can my circuit diagram be modified ?

    1ST 555 is to function as a toggle or flop flop with each press of the leaf switch/momentary switch.

    The 2nd 555 is a bistable ,triggered by the 1st 555.But the bistable's reset pin has a power on reset attached to it (and no switch as there isn't a need for one) ,to stop it from being triggered when i switch on power(which was happening 50% of the time).

    I can't use a monostable ,as it's stable state is 0 and my connected device will not work properly if "left" in a low 0Vss state!
     
  4. bigsanta11

    Thread Starter Member

    Feb 6, 2008
    14
    0
    Just a correction from my first post;

    So far i haven't been able to work out how i can use this leaf switch in place of the one on my breadboard.Only by cutting the leaf switche's 5Vcc trace to the device's IC and using the Vss from the output of the 555 as a reset signal works thus far,but i'd prefer to not cut the trace ,just incorporate the leaf switch somehow.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    I still don't know what you are trying to accomplish. My interpretation of a leaf switch is just a momentary contact switch, so focusing on it to much is distracting. If it is equivalent to a toggle switch you need to clarify.

    The first 555 is already a bistable. My bistable is a variation of yours.

    [​IMG]

    It will already capture and hold the state every time the button is pushed, it is a toggle flip flop. So what is the second 555 for?

    There are several ways to do set/reset with a 555. The reset is obvious enough, but if you need a circuit to capture and hold a transition this will do it (and is a variation of the first design).

    [​IMG]

    For easier access I'm modifying the OP's print for a smaller footprint and posting it here.

    [​IMG]

    One major mistake I see is the input on #2 (pin 6) has been left open. This is not a legal state. Normally it is connected to pin 2, but it is not clear what you are trying to do. It looks like an inverting Schmitt Trigger more than anything else, depending on how you connect Pin 6.

    .
     
    Last edited: Sep 26, 2010
  6. bigsanta11

    Thread Starter Member

    Feb 6, 2008
    14
    0
    To clarify .

    555 #1 .output will be used to switch to one of two states on a device.

    It has a signal pin,when this signal pin is connected and held at ground it switches mode to run at 60hz (ntsc tv standards).But if the signal pin of the device is held above 0Vss ,(3-5Vcc) then the device switches from 60hz to 50hz UK tv standard.To be controlled from the momentary switch of my device ,which at the moment operates as a reset button to reset/reboot the console .It is held at 5 Vcc when open ,but sends a gnd signal when it is closed (how would i connect this switch to #1 555 and use it to control all 555s)

    A bi colour LED will be used in the final circuit ,to show which of these (50/60hz) modes is selected by the user!



    #2 555 operates two other modes on the console,but needs the 1st 555 to control the output of #2 555.

    #2 555 needs to hold/have it's output state at gnd when i switch on power to the console and the circut,and keep this state until i press the momentary switch of the 1st 555 which will then change the 2nd 555's output to high (3 to 5Vcc) .This high state will be then be unchangeable .

    This is exactly what the 2nd 555 is controlling;
    When my console device is switched on ,with a gnd signal going to it's IC,(using a power on reset circuit to prevent the 555s switching states due to the consoles power on spikes)the console runs in english text mode, but then it has to receive a permanent and locked (stable)to high signal of between 3 to 5 Vcc after 1 second to work properly(any more presses of the momentary switch will be ignored by #2 555),otherwise it will have stability problems .

    Now if i turn on my console and the 2nd 555 is at a locked (stable) high state of between 3 to 5Vcc ,then it will start in Japanese text mode and have no stability problems (again,any more presses of the momentary switch will be ignored by #2 555) and #1 555 is still free to toggle between the consoles 50/60 hz modes.

    You see how difficult that last one would be, to show whether japan or english mode is active with the use of an LED on the output.If the LED action isn't possible,it can just be omitted from the circuit!

    Is that clearer ?


    #2 555 acts as bistable but as if it only had a trigger switch and no reset (pin 4) action can be activated by the user.Again,the 1st 555's momentary switch /output controls the 2nd 555's trigger control .
     
    Last edited: Sep 26, 2010
  7. bigsanta11

    Thread Starter Member

    Feb 6, 2008
    14
    0
    Right,i wired up your variation circuit to the output of the 1st 555 ,but removed the C1 R3 and the toggle switch and it's working exactly as i wanted it to ,minus the LED behaviour that shows whether english text mode /jap text mode is active ,as that's another ,slightly tougher problem altogether.

    I did find by accident when i was re wiring the 1st flip flop,that when i held the momentary switch ,the flip flop kept toggling from high to low and would stay on either (controllable )state when i let go of the switch,which was actually a behaviour i would have liked to kept,but i then rewired the circuit again correctly and lost how i made that happen ?

    Any clues how i did that?
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    I'm betting intermittent connection. Protoboards can be bad about that (and the fact they are made much cheaper doesn't help).

    So are you good now?
     
  9. bigsanta11

    Thread Starter Member

    Feb 6, 2008
    14
    0
    Not quite.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Don't know, there isn't enough information on that schematic to judge. What are you trying to do?
     
  11. bigsanta11

    Thread Starter Member

    Feb 6, 2008
    14
    0
    I can't quite believe this,but i can't get this action to happen again,and i've been over and over these circuits many times ,but can't see what i've missed.

    The first 555 bistable correctly filp flops with each press of the momentary button,but 555 #2 doesn't stay permanently in set mode(high) anymore once 555 #1's output triggers it,instead both just keep flip flopping with each button press. :confused:

    Well that's what i get for dismantling the working circuit ,ready for solder work.
     
    Last edited: Sep 30, 2010
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