Remote start switch

Discussion in 'Automotive Electronics' started by ProfessorZAPPP, Nov 20, 2015.

  1. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    Hello all

    i have prepared my cars electrical system for a remote starter switch to be inputted. also ran some micro/reed switch sensors on the gear lever and handbreak. all appropriate wiring in the vehicles loom has been identified and all run to the same point in the car.

    the starter is activated by my cars keyless entry button, instead of a large controller. once the keyless entry is pressed 3 times, i want the start process to begin provided the sensor circuits are in a closed state. wiring the ignition switch and sensors can all easily be done myself.

    I just need help on a 3 input switch that will output power..
    1.2.3 input pulses results in 1 output pulse, sounds simple enough to me but i just cant figure it out. latching relay setups, transistor switches and counter chips like the 4017 i have looked into but failed at making it work on a breadboard with leds (small scale)

    Any help, or guidance would be much appreciated
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Input the pulses to the 4017 counter. Monitor counter output 3 to detect the third pulse.
    The first pulse also triggers a reset one-shot to reset the counter after a given time (say a couple seconds).

    Edit: Below is a LTspice simulation of a circuit that, I think, does what you want.
    Output 3 goes high after 3 input pulses.
    Output 0 goes low at the first pulse and this resets the counter after about 2 seconds (as determined by the R1C1 time-constant).
    U3 provides an inversion to get the proper polarity for the Reset pulse and is a Schmitt trigger to give a reliable (longer) reset pulse.

    Note that power and ground for the IC's are not shown, which must be added.
    All inputs for the three unused gates on the U3 chip must be connected to ground.

    3 Pulse decoder.PNG
     
    Last edited: Nov 22, 2015
    DickCappels likes this.
  3. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    crutschow, dude thanks this is exactly what i was looking for!

    help me understand a few things though;
    where the input pulses V1 and V2 are shown to go into the 4017 chip, the contacts are not labled to which pins on the chip. R and C i assume are Reset and Clock. is the In pin just Vcc +3 - +15v

    And i plan on adding a small trimpot in place of R1on the reset to have an adjustable value to match my keyless entry time constant. which value do you think is too low to cause damage to circuit if possible? Would putting a 500k pot affect the normal functionality of the circuit or would it easily handle all resistance 0-500k only changing the reset time/charging of capacitor

    Thanks again for help
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    The CD4017 pin numbers are shown in the data sheet.

    Yes, R is the Reset input and C is the Clock input.
    The nominal logic levels go between 0V and the supply voltage of the ICs.
    What is the voltage of the pulse from the keyless entry?

    Yes, you can use a pot in place of R1.
    500kΩ should be fine.
    There is no lower limit to the resistance.
    You can also increase the value of C1 if you want a longer delay before reset.
     
  5. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    Awesome was just double checking.

    Voltage from keyless entry module is 12V (from car battery)
    the pulses are 1.5 seconds apart, and they are on for a total of 1 second
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    That means you want the reset to occur no sooner than 6s after the start of the first input pulse.
    A 500kΩ pot with a 33μF capacitor should allow you to set the desired reset time.
     
  7. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    How long will the output be on for, and will its voltage be the same as supply? as the data sheet for both 4017 and 4093 says 18v & 15v is their maximum working voltage, running this whole circuit off the cars battery direct would not fry anything right?

    By reset do you mean, after the chip receives 3 pulses, it will output on O3 as long as they are within 6 seconds of each other.

    Thanks for your help. I have everything set up on breadboards just need to pickup the 4017 chip tomorrow
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Yes, the chips' output voltages are the same as their supply voltages.

    To minimize the effects of any spikes on the vehicle power, I would add a filter to the power consisting of a 1Ω resistor in series with the battery power with a ≥100μF capacitor to ground between the resistor and the circuit.

    You stated the pulses were ON for 1 second with 1.5 seconds between pulses.
    That means the total time for the 3 pulses is 6 seconds, so you want the reset to occur after that, say 8 seconds or more, to make sure it doesn't reset before you get an output after the 3rd pulse.

    The output after the 3rd pulse will remain high until the reset occurs (or it receives another pulse before the reset).
     
  9. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    Everything makes sense to me on the theory side.

    I have all the components on the breadboard im just having trouble reading the circuit schematic, im not use to this type.
    at the top left of the 4017 there is the Reset, which i have connected. the Clock and the IN. is it drawn to say the Clock goes to ground, and the IN is where the pulses are connected to the +V pin 16 on the 4017?

    you said the power and ground for the IC's arent shown and need adding. So the 4017 pin 8 goes to ground. and the Power, pin 16 goes to +12v
    leaving the clock pin for the input pulses from keyless entry module?

    I know its a stupid question, but i want to be sure. Looking stupid is better than staying stupid
     
  10. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    After connecting all of the connections i believe to be correct all i can get to work is an LED flashing completely random and sometimes staying on until reset.
     
  11. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    If you are triggering the circuit from a mechanical switch you will need a debounce circuit.
    Also if nothing is connected to the clock you need a pull-down resistor (≈10kΩ) from the clock input to ground. You cannot leave high-impedance CMOS inputs open circuit as they assume arbitrary voltage levels due to leakage and stray pickup.

    The Clock Inhibit input goes to ground.
    IN goes to the Clock input.

    Don't understand your comment about IN pulses going to pin 16. :confused:
    That's where the power is connected, and the pulses go to the Clock input as you correctly stated in your last paragraph.
     
    Last edited: Nov 23, 2015
  12. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    I am triggering the circuit (its main power just from straight power in the car constant) do I still need a denounce circuit?

    The clock inhibit goes to ground? Which one is this, I can only see the clock pin on the 4017 pin out.

    Also you said of nothing is connected to clock it needs a pull down to ground, but isn't the clock connected to the pulses and the IN

    And the IN pin goes to the clock with the pulses connected together, but doesn't this go to ground also?

    I am obviously confused at how this setup works from pin out to breadboard but i am capable to do everything from this circuit onwards
     
  13. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    My answers above in red.
     
  14. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    That was for when the circuit is installed in the car, its voltages will all be 12v. For testing i am using power supply 5v through jumpers on Arudino board. When you say trigger you mean power the circuit? it will be always on while the car is locked or off and disconnected while car is running.

    Thanks, sorry my pinout says pin 13 is Enable.

    I have drawn a schematic of how i connected it i will be able to post tomorrow
     
  15. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Enable or inhibit are the same input.

    You seem to be confusing power with trigger. There's no relation between the two.
    Power is the steady DC voltage that powers the circuit, such as from the battery.
    Trigger is the pulse from pressing the remote that causes the circuit to count.

    Once again, how on the breadboard are you generating the trigger pulse?
     
  16. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    i am triggering the circuit with a +5V jumper connected to the breadboard supply, through a pushbutton switch and into the Clock pin 14 on the 4017 chip.

    on the 4093 i have connected pins 1 and 2 together at the same node as the diode, capacitor as shown in schematic. and pin 3 goes to the 4017's pin 15. all of the other inputs i have connected to ground (pins 5,6,8,9,12, and 13)

    both chips have power, +5v to pin 16 and 14 of each chip, and ground on 7 and 8

    i have disconnected and reconnected everything carefully and the led still blinks randomly, then pauses it sometimes latches, but its movements are random and uncontrollable at this stage?
     
    Last edited: Nov 25, 2015
  17. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    I have a feeling you are not really reading my posts since I seem to be repeating myself. :rolleyes:
    I will state (again) that you need a debounce circuit and a pull-down resistor on the clock input if you are using a mechanical switch to generate the clock.

    Please post your circuit as I previously asked. It will save us going in circles.
     
    djsfantasi likes this.
  18. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    I understand im sorry, i just thought if the desired working conditions of the circuit in the car was without a switch and just input, i should test with just input. i later added the switch for consistency/accuracy. read through debouncing page. it now works with the 10kohm and 10uf to ground on the clock.

    As my input in the car is not a mechanical switch, it is just a dead connection to the positive keyless entry, until the pulses are received. will the clock still need the debouncing circuit

    thanks for help sorry for confusion
     
  19. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    If the signal is a clean electronic pulse then you should not need a pull-down resistor or debounce circuit.
    The debounce circuit is only needed if mechanical contacts are generating the pulse since they bounce when closed and generate several fast pulses for each closure.
     
  20. ProfessorZAPPP

    Thread Starter New Member

    Nov 18, 2015
    21
    0
    ok thanks for all of your help, i will make the change from breadboard to PCB and connect appropriate relays etc.

    one last question about these CMOS configuration i now have, as there is 3 other unused gates on the 4093 i have grounded, is it possible to use them for other applications in the circuit, or do they need to be grounded.

    i ask because i have N/O and N/C contacts from reed and micro switches which i am going to wire through relays to cutoff the circuits start procedure if they are active (car in gear, no handbreak on)

    is there a way these unused gates can provide a voltage output to bypass whole circuit? if say the N/C contacts provided constant power to one gate could that gates output polarity be used for my application? and same for the N/O in reverse to another gate?

    if this cannot be done, i will just wire relays/contactors or power transistors to cutoff supply power to this circuit. i am trying to design the whole module to consume the least amount of power possible as its active whilst the car is switched off. Adding a voltage regulator to the supply may also be an option, if the chips can work at 5v, i will give them 5v and the relays they power will switch the 12v loads.

    Thank you for your time crutschow, really appreciate it
     
Loading...