This may have been asked before, maybe not to this specific amount.
I'm trying to design a timer module, for this specific application:
12 volts input is provided.
12 volts input is dropped. Timer starts counting.
one half of a second, +- 0.125 second, later the output does something. I dont care if it drops or is provided.
one second after count start, +- 0.125 second, ditto.
purpose: Traction control devices are expensive. Using accelerometer, I know exactly when we are slipping tires (drag racing). I want to retard the timing at 0 to 0.5 seconds (retard channel 1) and 0.5 to 1.0 seconds (retard channel 2).
The input is the transbrake switch- cuts the 12 volts to the Tbrake when the car launches. Thus, when this 12 volt is dropped, i want the timer to start.
The MSD box wants a ground to disappear, in order to activate the timing retard channels.
So, what I want:
channel 1: transbrake is engaged, charging resis/Capac circuit. transbrake released, RC circuit starts discharging, and after half a second, the output falls out. this de-energizes a relay, which disconnects the MSD terminal from ground.
channel 2: transbrake is engaged, charging resis/capac circuit. ransbrake released, RC circuit starts discharging, and after a full second, the output falls out. this de-energizes a relay, which disconnects the MSD terminal from ground
So for the first half second, both channels are active, then only one is, then none are.
Reason: I want to launch with the engine retarded 10 degrees. So Ch 1 and ch2 both have 5 degree chips in them. First half second, both are on, so 10 degree total. next half second, only ch 2 is on, so only 5 degree. after that, it's at the full 45 degree timing advance.
I've done a little reading, but I don't know much. I figure the relays will cost more than the components....
From my understanding, you bridge the resistor across the capacitor, to promote capacitor leak-down. The output will drop when the capacitor has drained itself empty. But I don't know how to predict Vmax of the capacitor. But from what I can tell, I can use the same capacitor # on both circuits, and just use a resistor that is twice as resistive for the 1.0 second delay timer?
(time) = (time constant)*(voltage)/(Vmax)
voltage = 12 VDC (actually 14.4 on the alternator
0.5 = TC * V/Vm
1.0 = TC * V / Vm
(time constant in seconds) = (resistance in ohms) * (capacitance in farads)
thus,
0.5 = (resistance in ohms) * (capacitance in farads) * 13.8 [avg] / Vm
1.0 = (resistance in ohms) * (capacitance in farads) * 13.8 [avg] / Vm
I'm trying to design a timer module, for this specific application:
12 volts input is provided.
12 volts input is dropped. Timer starts counting.
one half of a second, +- 0.125 second, later the output does something. I dont care if it drops or is provided.
one second after count start, +- 0.125 second, ditto.
purpose: Traction control devices are expensive. Using accelerometer, I know exactly when we are slipping tires (drag racing). I want to retard the timing at 0 to 0.5 seconds (retard channel 1) and 0.5 to 1.0 seconds (retard channel 2).
The input is the transbrake switch- cuts the 12 volts to the Tbrake when the car launches. Thus, when this 12 volt is dropped, i want the timer to start.
The MSD box wants a ground to disappear, in order to activate the timing retard channels.
So, what I want:
channel 1: transbrake is engaged, charging resis/Capac circuit. transbrake released, RC circuit starts discharging, and after half a second, the output falls out. this de-energizes a relay, which disconnects the MSD terminal from ground.
channel 2: transbrake is engaged, charging resis/capac circuit. ransbrake released, RC circuit starts discharging, and after a full second, the output falls out. this de-energizes a relay, which disconnects the MSD terminal from ground
So for the first half second, both channels are active, then only one is, then none are.
Reason: I want to launch with the engine retarded 10 degrees. So Ch 1 and ch2 both have 5 degree chips in them. First half second, both are on, so 10 degree total. next half second, only ch 2 is on, so only 5 degree. after that, it's at the full 45 degree timing advance.
I've done a little reading, but I don't know much. I figure the relays will cost more than the components....
From my understanding, you bridge the resistor across the capacitor, to promote capacitor leak-down. The output will drop when the capacitor has drained itself empty. But I don't know how to predict Vmax of the capacitor. But from what I can tell, I can use the same capacitor # on both circuits, and just use a resistor that is twice as resistive for the 1.0 second delay timer?
(time) = (time constant)*(voltage)/(Vmax)
voltage = 12 VDC (actually 14.4 on the alternator
0.5 = TC * V/Vm
1.0 = TC * V / Vm
(time constant in seconds) = (resistance in ohms) * (capacitance in farads)
thus,
0.5 = (resistance in ohms) * (capacitance in farads) * 13.8 [avg] / Vm
1.0 = (resistance in ohms) * (capacitance in farads) * 13.8 [avg] / Vm
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