Aftermarket Headunit improved "Illumination" detection

I have a Pioneer Z140-BH headunit, but AFAIK, most aftermarket headunits behave similarly. They have an "illumination wire" that tells the unit whether it should display "daylight mode" or "night mode". This wire is tapped into the car's wiring (typically a tail light or some other light that is on when the car's lights are on. So the sensor is either ON (+12v) or OFF (~0v) - probably some arbitrary threshold determines the boundary. On my Pioneer , the behavior for "night mode" is two-fold: it dims the display to a configurable night-time brightness. In order to view the screen during daylight the brightness must be set to a level that would be distracting at night. it optionally inverts the map display backround from white to black. This feature can be turned-off in the settings. Both behaviors are triggered by the "illumination wire" current. On my car, the wire is tapped off the tail lights. Now comes my problem. Many times I've needed to turn on lights in daytime due to rain, fog, or personal preference. Sometimes I like to drive with the grill led lights on - like many of the newer cars. Also the DRL setting on my US car (with stock halogens if that matters) also turns on the tail lights. Since the ambient light it is still kind of bright, the head unit screen is difficult to see. Now that I've added a rear camera, this annoyance has become a safety problem. Its really hard to see what's back there. So I decided I'd solve this problem by installing a photo-cell On/Off switch in the "illumination wire" circuit. "Night mode" will be only when the ambient light level is low enough to warrant it. Now my 2010 Cayman is a base model with very few options. No Bose, auto headlights, self-dimming mirrors, digital climate control. No fancy factory do-dads to cause maintenance headaches when they inevitably fail. I always wondered what the purpose was for that little wart on the (empty) bose center speaker grill. Sure looks like a sensor. Perfect place for one too. I looked in the PET and sure enough - it was called "sun sensor" (997.653.251.00). And the wiring diagram said it was connected to the climate control unit. So I popped the grill off to take a look. The two wires coming out of the sensor matched the wiring diagram document. Blk/Red and Brn/Wht. As expected Brn/Wht was connected to a ground somewhere. Blk/Red later became Gry/Grn and went to pin 8 on the Climatronic Control Unit. Fine, but I've only got the plain old manual A/C & heater controls. Couldn't see what sun had to do with that (or even the fancy Climatronic one for that matter). So I started thinking that I could high-jack this baby and use it tp be my photocell illumination switch. Run a few wires and problem solved! However, before cutting and running wires, I thought I'd do more research. Seems the sensor is sourced from Hella . Their web-site showed an almost identical sensor with some supporting documentation. It explained its purpose and function. Sun sensor General One of the sensors that is part of nearly every climate control unit nowadays is the sun sensor. Mostly located on top of the dashboard near the windscreen. The sun sensor measures the suns`s radiation and heat which causes the vehicles interior and its occupants to heat up. The sensor (on some vehicles two sensors are used) sends the measured value to the control unit, which directs cooler air in the vehicle interior. Function The sun light falls through a filter and an optical element on to a photocell. Photocells are sensitive semiconductor elements. When minimum light falls on the sensor there is a low current flow. If the light intensity rises, the current flow also rises. The contol unit recognises, through the current flow, how strong the light intensity is and manages the temperature flaps and the blower adjustment accordingly. On models with two sun sensors, the vehicle side where the stronger sunlight falls is cooled down more. ​ So, according to this - the "sun sensor" isn't an On/Off switch, but a variable potentiometer (resistor). That's not what I'm looking for. It would require some logic to interpret the on/off threshold and a relay to activate the headunit's trigger (illumination) wire. Still don't know why I need it with my dumb manual controller. I wonder what happens if I remove it? TBD Issues to be resolved: finding a suitable 12VDC photocell switch. figuring out where to install it. Mostly depends on the size and shape of #1. I've found a simple and small photocell switch on Amazon. Mixed reviews but the thing looks promising uxcell® DC 12V Photoelectric Switch Sensor Relay Module It has a 20" lead from the very small sensor to the logic board. I believe the sensor itself would easily co-exist with the existing sun sensor, and the module could stay under the dash somewhere. So no issues with Bose or other equipment. And the module has configurable sensitivity - from always on to always off, and everything in between. So it can be calibrated specifically for the installed location. BTW - found the same thing on ebay for <$3. So I ordered one and am waiting for it to arrive from China. (to be continued)

Logic gate on a project board? Since the sun sensor is basically a photocell which puts out a variable voltage you can set the threshold for a +12v output to your head unit to whatever your desired trigger brightness is. Latch it so it doesn't flicker from brief bouts of dark from overpasses/clouds/whatever.

Thanks for the response. Yeah, I figured that was a possibility, and really simple for those knowledgeable enough to do it. But it's over my head and then there's the concern of interfering with the "normal" function of this sensor. Although I don't think it does much in my specific case (no auto climate control), I'd like a solution that works for all of us. So the 3 buck photocell switch looked easy, low risk, and could be removed quickly if necessary. I'll mention that this switch/relay has been reported to have an issue at the transition point where it goes on/off rapidly causing a buzz. There's a simple mod (adding a resister across 2 pins of the IC) that fixes it. Hey, whaddya want for 3 bucks? A bottle of wine?

So only one of my cars has had a daylight sensor - 2001 Nisan Maxima - and it worked not all that well to turn my headlights on and off. Worked well at the extremes, but in the broad crossover region where it can be really important, it had issues. Bright sunny early mornings would prompt it to turn on the headlights (and dim the radio display so I couldn't see it), then often when it was cloudy and rainy, the headlights would turn off. Since it falsed both ways, it was not a simple matter of adjusting the light level. I think the issue may have had to do with how wide an area of the sky the sensor saw and integrated. In any case, I'd suggest taping the sensor on top of the center speaker and checking it in varying conditions before a permanent install.

Danschy. I understand those issues. We also have them on my wife's SUV. So I turn off the auto headlight function. But in my intended application, I only want the switch to come on when it is past dusk. I mean pretty dark . I think the problem you stated had a lot to do with the fact that the sensor's main purpose was to control the headlights. The headunit's display change was just a side-effect. The manufacturer wanted the headlights to come on early - for safety and liability issues. BTW, in my case a bright setting or rising sun would make the display brighter - and easier to read. My main concern is that is will trigger off every time I drive under a streetlight. That would get annoying. So I'll need to tinker with the setting to get it right.

In addition to adding the hysteresis resistor to keep it from chattering, might want to add a capacitor at the comparator input to slow down the response so it doesn't switch due to a transient condition, like driving under a streetlight.

Re: Aftermarket Headunit improved "Illumination" sensor OK, I've got a solution to the initial problem. To recap, I started this thread to deal with aftermarket headunits which use the running lights to determine whether to change their display into "night mode". On my Pioneer AVIC, this not only dims the display to a level that is unusable for daytime driving, but also optionally inverts the map display to simulate nigh time. By relying on the vehicle's lights rather than actual ambient light, this can be both annoying and dangerous. By law in FL and maybe all states, you must turn on headlights during rain. This also precludes setting DRL in the OBC (since it basically turns on your lights all the time). So my idea was to wire-in an automatic optical sensor to use ambient light to control the headunit's illumination. My initial post suggested using the car's standard sensor in the center speaker grill. While this may be doable, there is a possible interference with the climate control. But more important for my concept, that is not an optimal place for this sensor. My reasoning is that it easily will pick up stray light. This isn't like controlling headlights, which you want to turn on before dusk. I want this "feature" to only dim the display when it is truly dark. That is when the headunit's brightness becomes a problem. So I looked for a sensor/relay that could be adjusted and mounted in a location that won't get much stray light (for example oncoming headlights or streetlights). I found several inexpensive circuit boards on Amazon (and elsewhere) that fit this requirement. The first one I tried had two issues. https://www.amazon.com/Photoelectric-Switch-Sensor-Relay-Module/dp/B01GKWCXJM/ref=pd_sbs_147_40?_encoding=UTF8&pd_rd_i=B01GKWCXJM&pd_rd_r=19MHWF8ZK8G9ZZ7293SN&pd_rd_w=PL3Jq&pd_rd_wg=tZ3df&psc=1&refRID=19MHWF8ZK8G9ZZ7293SN The adjustment range was inadequate. It could not be dimmed to the post-dusk light levels I desired. It had an annoying relay chatter when the On/Off thresholds were approached. Someone posted as solution to this requiring soldering a resistor between two pins on a surface-mounted IC. Seemed worth trying - but alas my soldering skills weren't up to the challenge and I ended-up ruining the board. Someone with better skills than me could probably get this to work. I liked the fact that the sensor had long leads so that the circuit board could be hidden and the sensor could be placed in an optimal location. many Chinese vendors seemed to be selling products nearly identical to this first board. For my next try, I decided to try another product. Hopefully it would overcome my two issues. This is what I ordered https://www.amazon.com/GEREE-Control-Switch-Photoresistor-Photosensitive/dp/B01FXFMQRQ/ref=pd_sim_147_1?_encoding=UTF8&pd_rd_i=B01FXFMQRQ&pd_rd_r=19MHWF8ZK8G9ZZ7293SN&pd_rd_w=Nk4gm&pd_rd_wg=tZ3df&psc=1&refRID=19MHWF8ZK8G9ZZ7293SN While the design is very similar, it was definitely a different implementation. In bench testing, I found that it solved both my previous concerns. A wide range of useful settings (via the pot) and no noticeable relay chatter. The wires to the photo-resistor were a little short for my tastes, but I extended them by about 12" to a little over 2 feet. Here is how I intended to use it. I should add that the board has two surface-mounted LEDs: red (power) and blue (relay activated). When the headunit was initially installed in my car, I ran a red switched +12V wire to the headunit from the fuse box. The headunit's Illumination wire also ran under the dash; beside the fuse-box; under the sill; and finally back to the left rear taillight fixture. So everything I needed was localized to area between the fuse box and the door. Later, I used the same red wire to power my rear camera. So I decided I'd also use this wire to power my sensor board. You'll see the 4 red wires crimped together in one of the pictures. I also would need +12V to feed through the relay to headunit's Illumination wire, so I jumpered from the DC input power terminal across to the relay's Common terminal. The black wire goes to a chassis ground point (conveniently located near the fuse-box). I used an orange wire to go from the relay's Normally Closed terminal and butt spliced it to the headunit's Illumination wire - and disabled the connection to the taillight. Finally, I decided to try placing the photo-resistor in the seam between the dash and the A-pillar. This location would be relatively sheltered from stray light. Next, I decided it required an enclosure to contain an protect the circuit board. I used the smallest one I found at Radio Shack. the board is about 2.5" x 1.25" x .75". The Radio Shack enclosure is a little longer and wider than I wanted. Amazon has some slightly smaller (and cheaper) but only in quantity or 5. So I figured I could live with a slightly larger one. Here is the circuit inside the enclosure. For now, I left the cover off. I've left the fuse cover and carpet off for the time being so I can fine-tune the sensitivity. So far it seems to working exactly as I wanted. I thought about adding a cap to the relay output to damper rapid changes but so far I haven't found that necessary.

Re: Aftermarket Headunit improved "Illumination" sensor A couple more pics that I couldn't add to the previous post: I'm sure I've done a lousy job explainig all this, so I'll gladly answer any questions. It does assume a certain level of familiarity with the headunit's installation and rudimentary circuity, Don't let that mass of wires in some photos scare you, there's really only 4 wires involved (+12v red; black ground; orange illumination; sensor pair).