Car parking sensors; how do they work? - Page 1
Forum section: electronics / beginners

author: Sprutbærsj
author_rank: Contributor
timestamp: July 21, 2015, 03:11:40 pm
content: Hello.I have some ultrasonic rangefinders on my desk, and I have no idea how to make this bird sing. It has one white and one black wire, all glued shut/epoxy'd in a case and no datasheet.I have seen people reverse engineer these kits you can get on ebay,http://karve.in/?p=61, but I have not found one that can remove the existing module all together and only use the sensors.My tools are somewhat limited. A Fluke 89IV and a 35MHz analoge scope.If it is anyway relevant, I measured 20k ohm between the pins. Starts at 40k and drops to 20k in about 3 secoundsCan anyone point me in the right direction?http://gyazo.com/904ab101d1a7a30ee1acd23cb8ec16d6http://gyazo.com/49f650c66076f196b604d89c8c9b7c06http://gyazo.com/1d29031b5ff867897da76ba965b85728

author: poot36
author_rank: Frequent Contributor
timestamp: July 22, 2015, 04:22:57 am
content: I suspect that it is just a ultrasonic peizo transducer in there. You will need somewhere between 12 and 50 volts or so to drive it. How it is used in the car is the control module sends a short pulse to the transducer and then listens for a response to the ping it sent out earlier and from this can compute how far or near an object is. Try driving it with a 12V square wave and place another unit facing the circular part of it and connect that to your scope and you should be able to receive the square wave.

author: Sprutbærsj
author_rank: Contributor
timestamp: July 23, 2015, 01:30:36 pm
content: Quote from: poot36 on July 22, 2015, 04:22:57 amToday I finally pulled my left elbow out of my ass and did some testing because I couldn't find the solution using google.So right of the bat I decide I'll use an Arduino for the pulse, even though I have at least 20 unused 555 laying around, and write the simplest code I could imagine;Code:digitalWrite(3,HIGH);delay(1);digitalWrite(3,LOW);delay(1);This sould be a hint at how bad I am at this stuff, even though I can't admit it myself, but its okay because I used pin 3 which is a PWM.I try to use an N-channel mosfet in what I believe is a P-channel setup, with the company of a 2n3904 transistor. Expected results acquired; nothing happened.After some half-assed troubleshooting I ditch the whole thing and force my way in dry and screaming; arduino straight to the sensor. Unexpected results aquired; I got feedback from sensor 2!So now I have the sensor running at 5V ?Hz and ?A. How can this go wrong?I dunk the 2n3904 back in and try to use a external powersource, but expected results again!! ; now nothings working!After unnecessary amount of time I only get the transistor to squeek 5 volts from collector to emitter and it dead stops rising there, even though I set the powersupply to 12V or higher.Same goes if I try a darlington transistor setup. Mosfet and transistor gave no square wave at all.What is the right way to do this? As a summary from above, I seem to have no idea of whats going on..Sensors clamped together facing each other:http://gyazo.com/a3ed6fcf42cde0b766671831292ce57eSendt signal (top) and recieved signal (other top);http://gyazo.com/6852f8c647a628a49f4b5f3c41b4e31chttp://gyazo.com/ce24058e8a6304d4c2995b34a0992668http://gyazo.com/994a90809e415017db3492af85d4ceb7http://gyazo.com/2d7bc3e3b50a4ece1cb22b3c7bf02ab7

author: McBryce
author_rank: Super Contributor
timestamp: July 23, 2015, 09:14:12 pm
content: If you want to experiment with them, you can connect them to an Arduino with something like this:http://www.micro-examples.com/pics/090-ULTRASONIC-RANGER-schematic.pngMcBryce.

author: Stray Electron
author_rank: Super Contributor
timestamp: July 23, 2015, 11:26:56 pm
content: Heathkit used to sell ultrasonic sensors like this about 35 years ago. They sold them separately and also used them in their Hero robot. There should be plenty of information about those on the internet. I've bought used but working automotive ones (Ford) off of Ebay for $25.

author: Sprutbærsj
author_rank: Contributor
timestamp: July 28, 2015, 06:54:56 pm
content: So yesterday I did some stuff and today I did some stuff.YesterdayI went to one of those car cemetery places (?) and asked around. I wanted a unit that controls the parking sensors so I might get some idea how the signals from the controller to the sensor itself looked like. The guy working there began, all smart and old, and told me I needed the exact same sensors and all of them in order to get the system up and running. "What does he know?" thought the arrogant nerd. I ripped a module off one of the three car with them still on in the whole lot (no Toyota). This was from a BMW. I though I might get at least some good data, even though I didn't collect any of the sensors. I did however snip some cables so I don't have to work like a gorilla to measure and connect wires.And like Dave says: Don't turn it on, take it apart! Only because I have no idea how to turn it on...The unit and its guts:http://gyazo.com/e396e37cc19665e3039fb83981fd312fCase text:http://gyazo.com/3a8cbb193a6bfee4e0dc9caa3b5b3622Guts:http://gyazo.com/05ec8b7287fffd7780138e3f17151944TodayI did not blow up my scope, multimeter, powersupply and hopefully not the board itself. This is usually more luck than I am used to.I started counting, something I should have done before I even got the thing. I counted all the way to 12. Three times(!!). Eliminating one plug for signal and power, I'm left with 24.24pins / 2per sensor = 12 sensors. Uh oh! 24pins / 3per sensor = 8. UH OH!http://gyazo.com/d0f467324b6ee7e5159f578d6a6e0bd1Looks like the hare I'm gutting is a rabbit!No way in the pacific are the two types of sensors compatible...Licking my wounds: "I can at least look at what this unit is sending out in terms of data." Wrong! Dead wrong!After finding what I believe is +12V and GND inputs (using horrible methods of reengineering) I set the scope up to all three pins and hope for the best. Results: no español compatible muertos!I got one steady +5V on one combination, but nothing indicating pulsing or traffic.I'm thinking the next step is to look at what the unit is trying to send to the on-board computer for the car it was in. Hopefully something that can be readable.. My hopes for that working are so low I consider dropping it.Is there any way to test if the board is healty?Is there anything I can try?Should I try to find a sensor that uses the 3 pins?Should I drop the whole board and try something else?

author: McBryce
author_rank: Super Contributor
timestamp: July 28, 2015, 07:29:57 pm
content: That's a cross-carline BMW PDC, however it's more than just a simple distance controller, it can control front and rear sensors (four each), two speakers and it's even connected to the body CAN bus. So there's an aweful lot in there that you don't need.McBryce.Edit: I think this is it's pinout...http://img.photobucket.com/albums/v728/FlipZam/Golf%20VI/PDC%20retrofit/4870223716_9a96c8f2b2_b.jpg

author: Sprutbærsj
author_rank: Contributor
timestamp: August 18, 2015, 06:04:27 pm
content: After one week vacation and one week being sick, I finally did some stuff...New toy:https://gyazo.com/da1a5f9dd01c0687b1c347929163f4b4New victim:https://gyazo.com/da1a5f9dd01c0687b1c347929163f4b4https://gyazo.com/dfe374735c2cd9930b64da341b74d9e1https://gyazo.com/9d060540b8f217b622a106ba0080351chttps://gyazo.com/55bbbfc13b10343281d2dff403b61358I started measuring the pins. Found that on the sensors, one of the two pins goes to ground (0,3ohm) and there are some odd 16 ohms between the two pins on A, B, C and D (when open. No sensor attached).The blue "Low High" pot on the left side is sensitivity.The four red "pots" I don't know what is, looks like some sort of tuning for each sensor "channel".Above are four S8050 transistors and a single 74HC4052 "Dual 4-channel analog multiplexer, demultiplexer" (U3).The square (U4) is a Atmel Atmega48pa if my eyes don't deceive me, 8.000 SJK crystal.Two small 8pin packages are N5532 (left, U5) and LM393 (Other left, U6).I'm guessing right side is power only, so I have not touched it. 7808 (U2), L7805CV (U1).After making sure my powersupply don't have common ground and earth; I connected the old scope to it.. So if anything happpens, it's not my Rigol that blows first.https://gyazo.com/d09df055eed07c17b594e144c0501eecIt's doing something! Time to try out the Rigol:https://gyazo.com/6ffa5eadb3c54934b4a392750c5cb911https://gyazo.com/fa0506595d6d361cdc4394169533397dCan't find any clear feedback signal..https://gyazo.com/fe31b1e255de1a4d6b3024a30017be79If I move my hand close to the sensor (10-15cm) I get a weak wave back. Consistant, but weak..https://gyazo.com/e521cbca9101f4d9ed70897038c695dahttps://gyazo.com/bc2fc4549cb9cf2c20b5d706c77f025cI don't look at timing between sensors just yet..I want to know if I can replecate this signal and pickup function.