Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
|
|||
|
|||
2005 Ford Transmission PRNDL Logic... need help please.
I am trying to activate a relay when the vehicle is in anything other
than Park. The transmission module sends out 5V @ 120hz with varying pulse widths. In Park, I read 0.71V with the meter and looks to be apprx 1/7th of the pulse on the scope (square wave). In Reverse, the pulse is measured at 1.6V of 1/3 of the pulse with higher voltages and pulse widths in N,D,2. I've tried using this to enable a small dc relay, but only get chatter (even in Park). I've been told I could do the following... RC Integrator - Unity-Gain OpAmp Buffer - Comparator How would this work? Any help is greatly appreciated. |
#2
|
|||
|
|||
On 31 Mar 2005 19:38:05 -0800, "Thomas" put
finger to keyboard and composed: I am trying to activate a relay when the vehicle is in anything other than Park. The transmission module sends out 5V @ 120hz with varying pulse widths. In Park, I read 0.71V with the meter and looks to be apprx 1/7th of the pulse on the scope (square wave). In Reverse, the pulse is measured at 1.6V of 1/3 of the pulse with higher voltages and pulse widths in N,D,2. I've tried using this to enable a small dc relay, but only get chatter (even in Park). I've been told I could do the following... RC Integrator - Unity-Gain OpAmp Buffer - Comparator I think you would also need a sample-and-hold. How would this work? Any help is greatly appreciated. I'd prefer a one-chip solution involving a PIC micro, eg a $3 PICAXE with on-chip BASIC. An intelligent chip could open up additional possibilities. Otherwise I'd opt for a discrete digital solution involving a 74LS123 retriggerable monostable multivibrator and a 74LS74 flip-flop. Here's my hand drawn attempt: http://members.optusnet.com.au/~fzabkar/PRNDL2.gif (7KB) I've assumed a period of 8.3 msec (=120Hz), and pulse widths of 1.2ms (1/7 x 8.3) and 2.8ms (1/3 x 8.3) for Park and Reverse signalling. I've also assumed the pulses to be positive going. The 74123 is triggered by the transmission pulse (P) and produces a negative reference pulse, P1 (2.0ms). P1 clocks the 7474 flip-flop on its rising edge, ie after 2.0ms. If pulse P is shorter than P1, then the input to the FF will be low, otherwise it will be high. The Q or Q* outputs can then be used to control a relay via a transistor. Cext and Rext are chosen so that ... 2.0ms = 0.45 x Cext x Rext. Rext = 5Kohm. I've selected a pulse width of 2.0ms because it falls half way between Park and Reverse. Values of Rext = 10K and Cext = 0.47uF would give an acceptable pulse width of 2.1ms. - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
#3
|
|||
|
|||
On Sat, 02 Apr 2005 13:19:42 +1000, Franc Zabkar
put finger to keyboard and composed: On 31 Mar 2005 19:38:05 -0800, "Thomas" put finger to keyboard and composed: I am trying to activate a relay when the vehicle is in anything other than Park. Oops, the relay driver transistor in my circuit should connect to the Q output of the 7474, not its Q* output. I would also add clamping diodes to the P input of the 74123: +5V ___ | _|_ /_\ 1N4148 | | P ---|-- 74123 | _|_ /_\ 1N4148 | _|_ Ground - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
CAX, CAD, CAM, CAE, electronics, EDA, LSI, PCB, FPGA, VHDL, & Other Design CDs ::::::: , updated 28/Mar/2005 | Metalworking | |||
requesting a hand up - read for your Mom [short message with Quotes] | Home Repair | |||
FS: Semiconductor Data Books | Electronics Repair |