Here's how you can make your own 'fake alarm' flasher for the OEM Alarm LED in the instrument panel
This is a commonly available 555 Astable circuit and additionally I have incorporated an automated switch that will turn the LED on when the ignition is OFF - and vice-versa.
So it can be left unattended, just plug in and forget about it.
There are really two 'blocks' to the schematic -
The first part is the Electronic Switch: the MOSFET Transistor is biased on by the 100k ohm resistor to Ground, switching the input voltage from the Constant Supply through to the Oscillator circuit. When the Ignition is turned on, 12V is connected via the 10k ohm resistor - this creates a voltage divider with the 100K and now the Gate voltage is raised close to the Source Voltage and turns off the Transistor.
The second part is the Oscillator itself - it is called an 'Astable' because as long as power is applied it will generate an output (from pin 3) alternating from high to low.
The 555 oscillator affords the versatility to control the duration of the 'on' cycle and also the 'off'. These times are controlled by selecting values for R1 & R2, in this case 47K and 470K in conjuction with the value of capacitor C1. The values selected result in an 'on' flash of ~ 0.3 secs and the period between each flash is ~ 2.3 secs. You can choose different values for these resistors if you want to change the duration and interval of the flashes. The values I picked look visually 'about right' for an alarm warning signal.
The output resistor R5 (1K ohm) limits the current to the LED.
Simply constructed on VERO strip- board, I have, for demo only, attached an LED - of course the output will be connected to the Alarm connector, as described above, and drive the Instrument panel LED directly.
Actually if I had left the board a little longer it could be glued onto the face of the connector shell itself to have it be rigidly attached.
Don't worry too much about understanding how it actually works - just replicate the layout as shown with the component list placed as per the image.
The notation I use for the Strip Board is that a 'purple dot' represents an opening of the trace - I simply use a small drill slightly wider than the trace and just run it on the appropriate hole like a counter-sink (on the copper side of course) and it will separate the trace on either side. The component layout is shown with components on the Top Side and the traces are on the underside. The Traces are in Green and there are some wire links on the top (component) side that are shown in Red.
The PIN #'s are those for the Alarm Bypass Connector. You can use the original bypass connector, or if making a new one be sure to add the jumper leads 1-2 and 3-5, as well as making the connections shown.
It has a duty cycle of about 3 secs with about 0.5 secs of that the on 'flash'. In the LED off phase the circuit draws about 8mA and about 17mA while it's on
So it's only averaging about 10mA - battery would sustain that for a very long time! i.e. No fear of this draining your battery while it's parked
Parts List is as per below - I have included part numbers from Mouser.
Most of these parts are pretty generic - almost all can even be found in Radio Shack - except for the MOSFET
There is quite a bit of latitude in the MOSFET selection and the Diode.
Parts List:
Connector Shell/Terminals - see first post
Q1 - VP2206 - P-Channel MOSFET -
U1 - LM555CN -
D1 - 1N4148 -
C1 - 10uF Tanatalum Capacitor -
C2 - 0.01uF Capacitor -
R1 - 47K Resistor -
R2 - 330K Resistor -
R3 - 10K Resistor -
R4 - 100K Resistor -
R5 - 1K Resistor -
http://youtu.be/ztvyLxG-97M
