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single pulse on/off latch relays


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KPierson 
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Posted: May 22, 2012 at 9:34 PM / IP Logged  
I would not rely on voltage drops of diodes. Use a voltage divider circuit for each output instead. With precision resistors you'll get much more predictable results.
Kevin Pierson
trbolexis 
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Posted: May 23, 2012 at 1:41 AM / IP Logged  
Would something like this on the Outputs of the CD4017B work?
single pulse on/off latch relays - Page 2 -- posted image.
oldspark 
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Posted: May 23, 2012 at 4:26 AM / IP Logged  
The 1N914 voltage drop varies with current and temperature.
But the above circuit with the diodes feeding linear trimpots should be ok.
The trimpots should be 50k, though 20k is probably ok (10k is too low).
The voltage for the 4017 will have to be ~6V or higher (if you want a 5V output - ie, diode drop at 0.1mA is ~0.5V & the 4017 output drops ~0.4V). An 8V supply should be ok.
The trimpots are connected as per your diagram - ie, between the 4017 output and 0V with the wiper to the ECU (via the 1N914 etc).
That circuit depends somewhat on the ECU input impedance, and assumes the input references to 0V/GND (ie, pulls "down").   
In retrospect, I'd use a PICAXE - eg, the 08M2 - where input pulses can increment its DAC output to 5V.
That's merely an 8-pin PIC-08M2 with 78L05 regulator (etc) and its 2 "serial" programming resistors. But then you need the serial interface for programming, and the program....
But the you simply program the increments, and there is no variation with temperature or trimpot stability
trbolexis 
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Posted: May 23, 2012 at 10:38 AM / IP Logged  
The ECU input is a 51k pull down if that changes any of the info provided. Thanks for all the help so far!
Are the diodes absolutely required in the above diagram? I figured they would be as each output is tied to a ground through a pulldown resistor.
trbolexis 
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Posted: May 23, 2012 at 11:56 AM / IP Logged  
Something like this? What would heat dissipation be like if I trim the 12V down to 1V using the trimpot? There isnt much current flow, so I'd imagine very minimal?
I am still new to all this, so I'm trying to grasp an understanding.
Thanks for all your time.
trbolexis 
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Posted: May 23, 2012 at 11:56 AM / IP Logged  
single pulse on/off latch relays - Page 2 -- posted image.
oldspark 
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Posted: May 23, 2012 at 4:54 PM / IP Logged  
The 20k to 50k was based on the 4017 outputs sourcing ~2mA minimum with a 5V supply. 20k was borderline at low voltage for a "low spec" device.
Assume 15V/20k = 15x15/20k = 12mW max. (ie, an extreme of 15V thru the smaller 20k pot for max current/power)
51k pulldown is good - ie, an ECU open circuit will be "GND", and the 51k is reasonably negligible to the trimpot, though some readjustment will be necessary "in circuit".
The diagram is correct but check the pin numbers.
The "first" output (0) is pin 3 which should be not connected if "default" is to be 0V. (IE - the 0V output is any time a 4017 output does not supply voltage...)
Pin numbering in "output order" is 3, 2, 4,7, 10, 1, 5, 6, 9, 11.
Remember to connect reset (15) to the output pulse you want to reset (ie, the output after your last "latched" output.
And pin 13 (Clock Enable) to GND.
Reset (15) might need to be an RC to ensure POR "Power-On Reset" ie - starts at 0 output (pin 3).
trbolexis 
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Posted: May 24, 2012 at 1:29 AM / IP Logged  
The only outputs should be, 1V 2V 3V 4V and 5V. Zero will never be a desired output.
Pin 1 on the 4017 will need to be tied to RST(15).
Ill put all this together on the breadboard tomorrow.
What would be an suitable rebouncing circuit? The high input to the device will be 5V. A 555 timer? Cap?
I've learned a great deal so far. Thank you!
trbolexis 
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Posted: May 24, 2012 at 1:44 AM / IP Logged  
Debouncing*
oldspark 
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Posted: May 24, 2012 at 3:14 AM / IP Logged  
Switch debouncing is a pain...
The safest is to use a Schmitt inverter like the 74HC14 even if you only need the one inverter...
But NOT a 74HC14 because it is limited to a max 6V supply - hence use equivalents like the CD40106 or MC145848. (Probably any "Schmitt gate" that can be powered by your 4017's supply voltage; "gate" means AND, NAND, etc.)    
A simple RC might work depending on how long the push is etc.
I dislike 555s for their high current consumption (10mA) and other issues. (I love them as a chip, but not for applications which are not strictly timer or frequency applications.)
Have a look at these sites for ideas: all-electric debounce, ikalogic de-bouncing-circuits, & eetimes Solving-Switch-Bounce-Problems.
The trick is if your switch output is +5V, something that can debounce that yet be high enough for the 4017 "high" clock...
Since the 4017 must be powered from higher than +5V in order to output +5V to the EMS/EFI...
You might begin to see why an 8-pin programmable chip is easier for this sort of circuit. The debounce is thru software, the output voltage is from the "clock" incrementing its DAC output in 1V increments...
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