[Fwd: [M] Knock Sensor testor]
Joe Boucher
BoucherJC at lmtas.lmco.com
Mon Nov 2 20:08:32 GMT 1998
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Here is an interesting circuit from the Merkur list:
A recent thread concerns the possibility of the knock sensor (KS)
getting
tripped inappropriately, before actual detonation is occurring, with a
resulting reduction in performance due to the engine management system
retarding the timing. The question came up of how to test the KS.
If anyone is interested, here's a little inexpensive circuit which will
flash an LED whenever the knock sensor is "tripped". Thus, you can check
out the operation of the KS under actual operating conditions while
driving
the car. It may be useful to get a sense of under what conditions the KS
starts getting tripped.
+ 9V battery
o
|
1.2K 10K |
|-----\/\/\/--o--/\/\/\------o
--- | | 4
/// | |----------|
Gnd | 3| |
|-------->| | + -
| LM324 |---->(LED)--|
2| | 1 |
From KS (+) >---------------->| | |
|----------| |
| 11 |
o------------------|
|
---
/// Gnd
Parts: 1 10K 1/4W resistor 5%
1 1.2K 1/4W resistor 5%
1 Any LED (a "superbright' is easier to see)
1 LM324 op-amp (Radio Shack)
1 9V battery
All these parts are very common, and can be gotten at a Radio Shack.
Total
cost should be under $5. The battery will be the most expensive item.
The
numbers refer to pin numbers on the LM324. Unused pins are left
unconnected. The circuit can be built on a piece of "perfboard" or
similar
(Radio Shack) or the parts can be simply glued onto a piece of plastic
or
something and the connections made by soldering thin insulated wires
"point-to-point". The LM324 can be glued upside down on the plastic
(dead-bug technique).
On my XR4Ti the nominal voltage fed to the KS is about 2.5 volts. The
two
resistors will give about 1 volt to the LM324 at pin 3. Then, whenever
the
voltage on the knock sensor drops below 1 volt (KS activated), the LED
will
flash.
To use, keep the gizmo with you in the car, and run a long wire to the
(+)
terminal of the KS. Any wire will do, can be small gauge. The two
grounds
(Gnd) of the circuit should be connected together and also connected to
the
chassis ground of the car. So, you'll have two wires coming off the
circuit, one going to the KS, and the other going to chassis ground of
the
car. Now, while driving the LED will tell you when the KS is getting
tripped. A "superbright" LED will be easier to see in the daytime.
Disclaimer: I haven't built and used this circuit in my car yet. I
_have_
built it on the bench and it worked there. If anyone wants to try it
out,
I'll be happy to help out if there are any questions. Please email me
off-list. Thanks!
Steve
-------------------------------
Steve Roberts
sroberts at sunstroke.sdsu.edu
619 454 5234, 619 454 7008 FAX
-------------------------------
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Date: Sun, 01 Nov 1998 13:44:51 -0800
From: Stephen Roberts <sroberts at SUNSTROKE.SDSU.EDU>
Subject: [M] Knock Sensor testor
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A recent thread concerns the possibility of the knock sensor (KS) getting
tripped inappropriately, before actual detonation is occurring, with a
resulting reduction in performance due to the engine management system
retarding the timing. The question came up of how to test the KS.
If anyone is interested, here's a little inexpensive circuit which will
flash an LED whenever the knock sensor is "tripped". Thus, you can check
out the operation of the KS under actual operating conditions while driving
the car. It may be useful to get a sense of under what conditions the KS
starts getting tripped.
+ 9V battery
o
|
1.2K 10K |
|-----\/\/\/--o--/\/\/\------o
--- | | 4
/// | |----------|
Gnd | 3| |
|-------->| | + -
| LM324 |---->(LED)--|
2| | 1 |
From KS (+) >---------------->| | |
|----------| |
| 11 |
o------------------|
|
---
/// Gnd
Parts: 1 10K 1/4W resistor 5%
1 1.2K 1/4W resistor 5%
1 Any LED (a "superbright' is easier to see)
1 LM324 op-amp (Radio Shack)
1 9V battery
All these parts are very common, and can be gotten at a Radio Shack. Total
cost should be under $5. The battery will be the most expensive item. The
numbers refer to pin numbers on the LM324. Unused pins are left
unconnected. The circuit can be built on a piece of "perfboard" or similar
(Radio Shack) or the parts can be simply glued onto a piece of plastic or
something and the connections made by soldering thin insulated wires
"point-to-point". The LM324 can be glued upside down on the plastic
(dead-bug technique).
On my XR4Ti the nominal voltage fed to the KS is about 2.5 volts. The two
resistors will give about 1 volt to the LM324 at pin 3. Then, whenever the
voltage on the knock sensor drops below 1 volt (KS activated), the LED will
flash.
To use, keep the gizmo with you in the car, and run a long wire to the (+)
terminal of the KS. Any wire will do, can be small gauge. The two grounds
(Gnd) of the circuit should be connected together and also connected to the
chassis ground of the car. So, you'll have two wires coming off the
circuit, one going to the KS, and the other going to chassis ground of the
car. Now, while driving the LED will tell you when the KS is getting
tripped. A "superbright" LED will be easier to see in the daytime.
Disclaimer: I haven't built and used this circuit in my car yet. I _have_
built it on the bench and it worked there. If anyone wants to try it out,
I'll be happy to help out if there are any questions. Please email me
off-list. Thanks!
Steve
-------------------------------
Steve Roberts
sroberts at sunstroke.sdsu.edu
619 454 5234, 619 454 7008 FAX
-------------------------------
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