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The completed prototype ready for testing.
This circuit has been fitted to my partners’ 2009 VW Golf mk6 where it performs perfectly. When the reversing camera was first fitted with power taken directly from the Reversing Light it only worked when the engine was off. After some research I discovered that the lighting control computer was running the reversing light with battery +12V at 100% pulse width, fully On. But when the engine was running the alternator increased the system voltage to +14.2V and the Lighting Control Computer changed the pulse width to ~75% which was not good enough for the camera which then shut down.
So some background information then to this simple, cheap circuit -
Modern vehicles control the brightness of filament light globes by sendingpulses of battery voltage at ~100 pulses per second, with varying pulse widths. (Slower pulse rates may produce visible flicker,faster destroys globes as the on/off magnetism in the ‘coiled coil’ filament shakes itself to bits). LEDs are usually operated at just200 pulses per second to avoid creating electromagnetic interferencein other systems. These slow pulse rates also provide relatively large testing time windows for Lighting Control Computers.
Lighting Control Computers are factory adjusted to provide the correct ‘type’of powering for LEDs, Filament globes, High Intensity Discharge, etcand they monitor the load and do tests for open or short circuits,etc, even when a light is OFF. There is very little spare power available from each output and the system may object to any extraload.
Lighting Control Computers maybe ‘field adjusted’ when lighting is changed. This usually requires a computer connection to the vehicle’s On Board Diagnostics (OBD) interface and a specialist (and often proprietary) program.
Bulbtest pulses sent from Lighting Control Computers normally are very low power <1mA for <10%of a pulse period to avoid producing a ‘flicker’ which works outas 1 / 100 / 10 = 1 /1000 s. A simple electronic filter / detector made from a diode, a resistor and a capacitor can easily reject test pulses while integrating and detecting multipulse signals.
Itis easy to install a rear view camera on older vehicles where the Reversing Light globes just receive switched battery voltage. Plenty of spare power is available and the vehicle’s systems won’t notice the slightly increased load. Look on the internet for anynumber of ‘how-to’ descriptions for general installation.
Arough-and-ready work-around for powering a Reversing Camera from a pulsing signal is to fit a relay across a reversing light to switch battery voltage to a camera. This works because the huge magnetic field required to ‘pull-in’ the mechanical relay switch doesn’t fade away much between continuous pulses and the inertia of the mechanism just stays where it is. Occasional, single, Filament Test pulses are too short low in power to pull-in 12V relays that typically require >100mA for >0.01s.
Up until 2006 relays worked fine in most vehicles, but many newer vehicle’s lighting computers will see the extra load as a short circuit and shut down the Reversing Light. So a much, much lower power solution is required for piggy backing on the Reversing Light’s Pulsing signal.
Here is a low power, low cost Switching device that only takes ~0.5mA of activation power. Basically the circuit steals and smooths just enough power to operate a solid state switch (constructed from 2 cheap transistors) to pass full battery power to the camera. It taps into the wire carrying PWM to a Reversing Light, it also needs a source of battery voltage (Acc or Run) and a Ground.
Here are the building blocks for the circuit -
+12VIN
Pulses--> diode isolator --> current limiter --> storage capacitor--> voltage burner --> transistor switch(es)
+12VOUT
Total cost under AU$5 (cheaper than a relay). But many of the parts arenot available in single quantities, so it’ll cost a bit more if you only build one.
[Note– these are ‘X-Ray’ views of the circuit boards, when makingthe cuts imagine a mirror image (swap left/right)]
Parts List (parts numbered from left to right & top to bottom acrossstrip board)
Stripboard 8 rows x 9 holes with 2 track cuts
[DiodeSw IN 1N4002 small signal or rectifier type]
Capacitor1 10uF 25V electrolytic, -ve down (higher voltage Ok, but not lower)
Resistor1 27k quarter Watt
Diode1 1N4002 small signal or rectifier type
Resistor2 1k oneWatt
Diode2 1N4002 small signal or rectifier type
Transistor1 top BD136 PNP low power type in TO126 case, or small signal type inTO92 case
Transistor2 bot 2N2222 NPN small signal type
Resistor3 4k7 quarter Watt
Resistor4 10k quarter Watt
Resistor5 10k quarter Watt
‘Helper’Wire ~35mm Solid copper strand from household power cable
Alternates
Diodes anysmall signal or small rectifier types, eg 1N4148, 1N4001, 1N4004, etc
BD136 anylow/medium power PNP, with BCE pinout egBD136, orwith CBE pinout, egBC327, etc
2N2222 anysmall signal NPN, with CBE pinout pattern, eg BC347, BC337, P1000*,etc
Prototype used 1N4002, BC327 and P1000. With 120mA load no heating detectableduring continuous 24hr test.
2 slightly different component positions for different pinouts of the PNP transistor
Enjoy
This circuit has been fitted to my partners’ 2009 VW Golf mk6 where it performs perfectly. When the reversing camera was first fitted with power taken directly from the Reversing Light it only worked when the engine was off. After some research I discovered that the lighting control computer was running the reversing light with battery +12V at 100% pulse width, fully On. But when the engine was running the alternator increased the system voltage to +14.2V and the Lighting Control Computer changed the pulse width to ~75% which was not good enough for the camera which then shut down.
So some background information then to this simple, cheap circuit -
Modern vehicles control the brightness of filament light globes by sendingpulses of battery voltage at ~100 pulses per second, with varying pulse widths. (Slower pulse rates may produce visible flicker,faster destroys globes as the on/off magnetism in the ‘coiled coil’ filament shakes itself to bits). LEDs are usually operated at just200 pulses per second to avoid creating electromagnetic interferencein other systems. These slow pulse rates also provide relatively large testing time windows for Lighting Control Computers.
Lighting Control Computers are factory adjusted to provide the correct ‘type’of powering for LEDs, Filament globes, High Intensity Discharge, etcand they monitor the load and do tests for open or short circuits,etc, even when a light is OFF. There is very little spare power available from each output and the system may object to any extraload.
Lighting Control Computers maybe ‘field adjusted’ when lighting is changed. This usually requires a computer connection to the vehicle’s On Board Diagnostics (OBD) interface and a specialist (and often proprietary) program.
Bulbtest pulses sent from Lighting Control Computers normally are very low power <1mA for <10%of a pulse period to avoid producing a ‘flicker’ which works outas 1 / 100 / 10 = 1 /1000 s. A simple electronic filter / detector made from a diode, a resistor and a capacitor can easily reject test pulses while integrating and detecting multipulse signals.
Itis easy to install a rear view camera on older vehicles where the Reversing Light globes just receive switched battery voltage. Plenty of spare power is available and the vehicle’s systems won’t notice the slightly increased load. Look on the internet for anynumber of ‘how-to’ descriptions for general installation.
Arough-and-ready work-around for powering a Reversing Camera from a pulsing signal is to fit a relay across a reversing light to switch battery voltage to a camera. This works because the huge magnetic field required to ‘pull-in’ the mechanical relay switch doesn’t fade away much between continuous pulses and the inertia of the mechanism just stays where it is. Occasional, single, Filament Test pulses are too short low in power to pull-in 12V relays that typically require >100mA for >0.01s.
Up until 2006 relays worked fine in most vehicles, but many newer vehicle’s lighting computers will see the extra load as a short circuit and shut down the Reversing Light. So a much, much lower power solution is required for piggy backing on the Reversing Light’s Pulsing signal.
Here is a low power, low cost Switching device that only takes ~0.5mA of activation power. Basically the circuit steals and smooths just enough power to operate a solid state switch (constructed from 2 cheap transistors) to pass full battery power to the camera. It taps into the wire carrying PWM to a Reversing Light, it also needs a source of battery voltage (Acc or Run) and a Ground.
Here are the building blocks for the circuit -
+12VIN
Pulses--> diode isolator --> current limiter --> storage capacitor--> voltage burner --> transistor switch(es)
+12VOUT
Total cost under AU$5 (cheaper than a relay). But many of the parts arenot available in single quantities, so it’ll cost a bit more if you only build one.
[Note– these are ‘X-Ray’ views of the circuit boards, when makingthe cuts imagine a mirror image (swap left/right)]
Parts List (parts numbered from left to right & top to bottom acrossstrip board)
Stripboard 8 rows x 9 holes with 2 track cuts
[DiodeSw IN 1N4002 small signal or rectifier type]
Capacitor1 10uF 25V electrolytic, -ve down (higher voltage Ok, but not lower)
Resistor1 27k quarter Watt
Diode1 1N4002 small signal or rectifier type
Resistor2 1k oneWatt
Diode2 1N4002 small signal or rectifier type
Transistor1 top BD136 PNP low power type in TO126 case, or small signal type inTO92 case
Transistor2 bot 2N2222 NPN small signal type
Resistor3 4k7 quarter Watt
Resistor4 10k quarter Watt
Resistor5 10k quarter Watt
‘Helper’Wire ~35mm Solid copper strand from household power cable
Alternates
Diodes anysmall signal or small rectifier types, eg 1N4148, 1N4001, 1N4004, etc
BD136 anylow/medium power PNP, with BCE pinout egBD136, orwith CBE pinout, egBC327, etc
2N2222 anysmall signal NPN, with CBE pinout pattern, eg BC347, BC337, P1000*,etc
Prototype used 1N4002, BC327 and P1000. With 120mA load no heating detectableduring continuous 24hr test.
2 slightly different component positions for different pinouts of the PNP transistor
Enjoy