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Car Parking Sensors Help Needed

Discussion in 'Sensors and Actuators' started by decetch, Sep 2, 2013.

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  1. decetch

    decetch

    8
    1
    Sep 2, 2013
    Hi Everyone,

    First post so I hope I explain this clearly enough for everyone. Absolute newbie to electronics.

    I intend to buy a car that's fitted with rear parking sensors. The problem is, I have a hearing loss in the high treble area and I can't hear the sound being transmitted. Is there a component on the PCB that produces the tone/pitch that can be changed to enable me to hear the sound? I asked the hearing consultant and she said I'd need something about 900 - 1000 hz.

    I hope I've explained this clearly enough. Thanks for your assistance.
     
  2. davenn

    davenn Moderator

    13,553
    1,852
    Sep 5, 2009
    hi detech
    welcome to the forums :)

    unfortunately you havent really given us anything much to go on there

    a model of car would be a good start --- some one here may be an auto electrician and has had dealing with the particular model
    otherwise, we would need to see the parking sensor processing board see what type of audible device it has, a circuit diagram would be extremely helpful too

    so if you can provide those things ... maybe ... just maybe some one can help you :)

    cheers
    Dave
     
  3. decetch

    decetch

    8
    1
    Sep 2, 2013
    Hi Dave,

    Thanks for the reply. I thought I might get that sort of response. The car is a 2013 Toyota Hybrid Camry HL. My guess is that the parking sensors are provided to Toyota by a contract manufacturer and maybe they don't have access to the PCB circuit diagram. I plan to ask Toyota if it's possible to get one but I won't hold my breath. I was probably asking, in hope, if the idea was feasible.
    It's hard to image that any dealership would play around with this stuff.
    In the meantime I'll try to find out what I can.

    Thanks Dave.
     
  4. duke37

    duke37

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    753
    Jan 9, 2011
    One possibility is to put a microphone close to the sensor speaker and trigger a crude oscillator running at a lower frequency.
    The sensor speaker may be too small to output a lower frequency so another speaker would be necessary.
    This option would mean that there would be no interference with the original system.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,267
    Nov 28, 2011
    I second Duke's suggestion. You should avoid modifying any part of your vehicle, if at all possible.

    You could build a self-contained device, powered from the car battery supply, that "listens" for the original sound (using an electret microphone or similar) and uses that signal to enable an oscillator at your desired frequency. The oscillator would drive a transducer or small loudspeaker.

    I can design a circuit to do this, but it's not a good first project for an electronics newbie, unless you have high general technical aptitude and resourcefulness. It would involve building a circuit up on stripboard (Google it) using a few ICs (integrated circuits) and other small electronic components. You would need to mount it in a case of some kind, and connect it into the car's electrical system. Let me know if you're interested.
     
  6. decetch

    decetch

    8
    1
    Sep 2, 2013
    Hi duke37 and KrisBlueNZ,

    Thank you both for your replies. Firstly, I know nothing about electronics at all. I was initially looking for a solution to this problem. If a solution was found, and it seems it has been, then I would have sought someone to build a new device or amend the existing system. I have asked Toyota if they can supply a circuit diagram of the PCB that controls the system. I'm yet to hear back. I like the idea of not altering/interfering with the original equipment.

    Kris I'd love to hear what you have in mind. Thanks.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,267
    Nov 28, 2011
    OK, here's a circuit that should do what you want.

    [​IMG]

    It's pretty straightforward, though it probably looks pretty complicated.

    If you're interested in understanding the circuit better, you can look up any unfamiliar words using Google or Wikipedia.

    The microphone on the left is an electret microphone - a small cylindrical microphone as used in dictation machines. You will need to put this close to the sound source on the existing unit.

    R1 provides operating current that's needed by the microphone. C1 couples the signal from the microphone into the amplifier stage built around Q1. This is a conventional common emitter amplifier with variable gain and high frequency boost.

    R6 adjusts the gain, and should be set so the circuit reliably detects the sound from the unit but is not false-triggered by other sounds.

    The amplified signal appears on Q1's collector (the top terminal) and is coupled into a charge pump circuit consisting of D1, D2 and C4. A voltage is developed across C4 that is related to the amplitude of the signal picked up by the microphone. When this voltage exceeds about 0.7V, Q2 turns on and pulls its collector high.

    This point in the circuit is labelled "TONE: H, SILENCE: L". These states are high (+9V) and low (0V) respectively.

    This control signal feeds a circuit built around U1, a CD4093B quad NAND gate with Schmitt trigger inputs. That's a bit of a mouthful, but it means that the device consists of four identical "gates" (shown as U1B, U1A, U1D and U1C) whose output is always high unless both inputs are high, in which case the output is low.

    These gates have a special kind of input circuit that means that a single gate (U1B in this case) can be used as an oscillator - a circuit that generates a continuous alternating signal at a particular frequency.

    The CD4093 has two power pins - pins 14 and 7. C6 is a "decoupling" capacitor, required for reliable operation of the IC, and should be connected as close as possible to those two pins.

    When Q2's collector is high, U1B is enabled and produces a signal at its output. The frequency of this signal is determined by R10 and C5. R10 is a variable resistor or "trimpot" that you should adjust to obtain the frequency (pitch) that you want in the speaker.

    U1A is used to invert (reverse) the signal, and U1C and U1D are used to gate the signal with the tone-present indication from Q2. Their outputs are fed to two simple complementary bipolar buffer stages which drive opposite ends of the speaker. When U1B's output is high, the Q3/Q4 output is high and the Q5/Q6 output is low. When U1B's output is low, the Q3/Q4 output is low and the Q5/Q6 output is high. This allows a voltage of up to about 15V peak-to-peak to be applied to the series combination of R11 and the speaker, so the speaker can be quite loud.

    R11 is a "select on test" resistor whose value determines the speaker volume. There are many variables involved here, such as speaker impedance, speaker sensitivity, speaker mounting, enclosure resonance, enclosure location, your ear's response, and so on, so it's best for you to try different values for R11. Start with around 100 ohms. Lower values make the speaker louder and vice versa. R11 may need to be a 1 watt resistor.

    The speaker needs to be located away from the microphone, otherwise you will get a situation where the circuit never turns off, because it "hears itself". This can be minimised by using a speaker with a large or heavy cone that cannot reproduce high frequencies well, mounting the speaker firmly so nothing rattles, and tightly coupling the microphone to the unit so you can reduce the circuit's sensitivity.

    If this proves to be an ongoing problem, you can add a capacitor directly across the speaker to reduce the high frequencies in its output. Initially try a few microfarads. Higher values will attenuate the high frequencies more and vice versa. The capacitor must be non-polarised.

    U2 is a voltage regulator that provides a constant 9V supply to the circuit. It is powered from the automotive +12V supply with R13, R12, and D3 added to protect it against high voltages during automotive load dump.

    I suggest you put the circuit in a strong plastic box with the speaker, and connect the microphone through a length of screened audio cable.

    The circuit can be constructed on stripboard, also called Veroboard in the UK. If you plan to build it, or get it built (e.g. by an electronics student, perhaps), let me know and I will write up a full parts list for Digikey. The components cost is not great - should be less than USD 25 excluding the stripboard and the loudspeaker.

    If you're not in the U.S. please enter your location in your profile and I will try to find an appropriate supplier instead of Digikey.
     

    Attached Files:

  8. decetch

    decetch

    8
    1
    Sep 2, 2013
    Hi Kris,
    Thank you for going to the trouble of designing a circuit that would suit my needs. You're a very clever person. Unfortunately, I've struck a few snags that might prevent using this type of thing.
    I was told that the speaker for the sensors was in the boot (trunk) of the car. This is not the case, it's behind the dashboard. I spoke with a technician at a local Toyota dealer this morning and he has been informed by Toyota that there is no space left behind the dashboard to fit anything else. I also want front parking sensors fitted but they don't have an accessory kit for those for that reason. The technician was going to check with Toyota again to see if anything can be changed so that I can hearing the speaker. Plus, I'm not all that keen to try and rip the dashboard out to have a look. I'll have to try and come up with another solution. If you can think of any other way that I can solve this problem I'd appreciate it. When I have the car delivered, which will probably be a few weeks away because they don't have the car that I want in stock, I will have a look at things and see if there's any space I can find to fit these devices.

    Thanks Kris for the trouble you've already gone to, I really appreciate it.
     
  9. duke37

    duke37

    5,337
    753
    Jan 9, 2011
    The closer the microphone is to the sound, the better but there is sound in the cabin to be heard and it can be sensed and amplified.

    If the sound level is low, it may be necessary to filter the signal to eliminate extraneous sound. If a filter is used, then it will need to be tuned to the sensor. Perhaps a 'geetah' player could tell you the frequency if Toyota likes to keep secrets.

    An electret microhone is very small and there must be enough room to fit it under the dash but I sympathise with the dealer who does not want to disturb it. Cars are not made to be repaired these days.
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,267
    Nov 28, 2011
    You're welcome. Don't worry if you don't use my design; it's searchable now so someone else may use it.

    Duke's idea might be workable. If the circuit responds to only the frequency that's emitted by the unit, with a very tight filter, it could be placed anywhere in the car. You would still need to power it somehow though. Perhaps rechargeable batteries.

    I hope you can work something out.
     
  11. decetch

    decetch

    8
    1
    Sep 2, 2013
    Thanks for your suggestion Duke, that might be worth a try. Is there any way I can measure the frequency emitted by the unit? I don't think I'd be able to get that info from Toyota.
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,267
    Nov 28, 2011
    There are lots of ways. The way I would do it is: record the tone using the voice recorder feature of a smartphone, transfer the recording to a computer, view it using a waveform editor (e.g. Audacity), measure the duration of, say, 20 (for accuracy) consecutive cycles, divide the duration by the number of cycles, and take the reciprocal of the result (to convert a cycle period into a frequency).
     
  13. duke37

    duke37

    5,337
    753
    Jan 9, 2011
    Kris has beaten me to it, they get up early in NZ.

    There are programs, perhaps even Audacity, which will do a Fourier analysis to see the frequency constituents of a waveform.

    I suggested getting a tame guitar player to estimate the note. There are also guitar tuners which can measure the frequency.

    If a filter is to be used, then the frequency should be constant or nearly so. The tighter the filter, the better.
     
  14. duke37

    duke37

    5,337
    753
    Jan 9, 2011
    Audacity can measure frequency.

    "The Enhanced Autocorrelation function is very good at identifying the pitch of a note."

    Edit
    I have tried to get information from Toyota they have a factory nearby) without success. To give an amswer they want country, model and chassis number.
     
    Last edited: Sep 5, 2013
  15. decetch

    decetch

    8
    1
    Sep 2, 2013
    Hi Everyone,

    Thank you all for your input. I've just been informed I can't get the car for about 6 weeks or so, therefore I don't have access to it to measure anything. I don't think it's a matter of Toyota keeping secrets. It's probably because they've never been asked for this information before and simply don't know. When I get the car and can find out how much room there is and can measure the frequency, I'll get back to you and we'll see what can be done from there. Thanks once again for all your assistance, I really appreciate it.
     
  16. decetch

    decetch

    8
    1
    Sep 2, 2013
    Hi Kris,
    I think I'll go with your design. I still haven't got the car yet but I'll get someone to build your circuit in advance. I'd appreciate a parts list for your circuit if possible.
    Thanks.
    Decetch
     
  17. duke37

    duke37

    5,337
    753
    Jan 9, 2011
    I had a talk with my neighbour who has an Audi. As an object is approached, the frequency of the beeps rises and eventually there is a constant tone.
    Also, the frequency of the note rises so that it would be difficult to make a narrow filter to select it.

    I have never played with audio signals but some radio amateurs now use SDR (software defined radio). The SDR programs can display the audio as a waterfall, showing the frequency changing with time.

    I had a look at a four pole Butterworth filter but do not think this will be suitable.
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,267
    Nov 28, 2011
    OK, I made a slight change to the circuit - I changed the speaker driver circuit from bridge-tied-load to single-ended. This reduces the maximum output power to the speaker but I think you will be fine with the changed design. The speaker I've specified has an SPL (sound pressure level) of over 90 dB at its rated output power.

    [​IMG]

    Here is a parts list with references to Digikey product pages.

    1x (C1) 6n8 capacitor http://www.digikey.com/product-detail/en/B32529C682K/495-4421-ND/2651653
    2x (C2,3) 68n capacitor http://www.digikey.com/product-detail/en/B32529C683K189/495-5021-1-ND/3881211
    1x (C4) 1 µF 16V electrolytic capacitor http://www.digikey.com/product-detail/en/ESH105M050AC3AA/399-6541-ND/3082956
    1x (C5) 22n capacitor http://www.digikey.com/product-detail/en/B32529C223K/495-2520-ND/1089800
    3x (C6,9,10) 100n capacitor X7R http://www.digikey.com/product-detail/en/C420C104K5R5TA7200/399-4491-1-ND/818348
    2x (C7,8) 100 µF 16V electrolytic capacitor http://www.digikey.com/product-detail/en/ESK107M016AC3AA/399-6601-ND/3083016
    1x (C11) 100 µF 35V electrolytic capacitor http://www.digikey.com/product-detail/en/ESK107M035AE3AA/399-6104-ND/2712510
    2x (D1,2) 1N914 diode http://www.digikey.com/product-detail/en/1N914ATR/1N914ACT-ND/1626125
    1x (D3) 1N5359B zener diode 24V 5W http://www.digikey.com/product-detail/en/1N5359BG/1N5359BGOS-ND/1474107
    1x (LS1) loudspeaker 8 ohm http://www.digikey.com/product-detail/en/AS06608PS-2-R/668-1268-ND/1745562
    1x (MIC1) electret microphone http://www.digikey.com/product-detail/en/CMC-5044TF-A/102-1723-ND/1869983
    2x (Q1,3) BC337-25 transistor http://www.digikey.com/product-detail/en/BC337-025G/BC337-025GOS-ND/1475621
    2x (Q2,4) BC327-25 transistor http://www.digikey.com/product-detail/en/BC327-025G/BC327-025GOS-ND/1475586
    1x (R1) 5k6 resistor http://www.digikey.com/product-detail/en/RNMF14FTC5K60/S5.6KCACT-ND/2617520
    2x (R2,8) 100k resistor http://www.digikey.com/product-detail/en/RNF14FTD100K/RNF14FTD100KCT-ND/1975158
    3x (R3,7,9) 22k resistor http://www.digikey.com/product-detail/en/RNMF14FTC22K0/S22KCACT-ND/2617471
    1x (R4) 10k resistor http://www.digikey.com/product-detail/en/RNMF14FTC10K0/S10KCACT-ND/2617809
    1x (R5) 2k7 resistor http://www.digikey.com/product-detail/en/RNMF14FTC2K70/S2.7KCACT-ND/2617483
    1x (R6) 200R trimpot http://www.digikey.com/product-detail/en/3362P-1-201LF/3362P-201LF-ND/1088415
    1x (R10) 100k trimpot http://www.digikey.com/product-detail/en/3362P-1-104LF/3362P-104LF-ND/1088413
    1x (R11) select-on-test resistor to set the speaker volume
    1x (R12) 33R 3W resistor http://www.digikey.com/product-detail/en/4-1625892-3/A105914CT-ND/3477464
    1x (R13) V18ZA40 varistor http://www.digikey.com/product-detail/en/V18ZA40P/F3078-ND/1009327
    1x (U1) CD4093B integrated circuit http://www.digikey.com/product-detail/en/CD4093BE/296-2068-5-ND/67329
    1x 14-pin DIP IC socket for U1 http://www.digikey.com/product-detail/en/1-390261-3/A100205-ND/1125623
    1x (U2) µA7809, LM7809 etc three-terminal regulator http://www.digikey.com/product-detail/en/MC7809CTG/MC7809CTGOS-ND/1481254
    stripboard (aka veroboard) see https://en.wikipedia.org/wiki/Stripboard

    For R11 you can initially use a 200 ohm trimpot the same as R6. When you've adjusted it for the volume you want, you may need to remove it, measure it and replace it with the closest available fixed resistor with a wattage rating of 1W, 2W or even more; the trimpot is only rated for 0.5W and may get hot.

    Edit: That's a really dumb way to control the volume. I realised this earlier but forgot to update the design. I'll post again shortly.
     

    Attached Files:

    Last edited: Oct 4, 2013
  19. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,267
    Nov 28, 2011
    Sorry, here's how I should have done it.

    [​IMG]

    Here is a parts list with references to Digikey product pages.

    1x (C1) 6n8 capacitor http://www.digikey.com/product-detai...421-ND/2651653
    2x (C2,3) 68n capacitor http://www.digikey.com/product-detai...1-1-ND/3881211
    1x (C4) 1 µF 16V electrolytic capacitor http://www.digikey.com/product-detai...541-ND/3082956
    1x (C5) 22n capacitor http://www.digikey.com/product-detai...520-ND/1089800
    3x (C6,9,10) 100n capacitor X7R http://www.digikey.com/product-detai...91-1-ND/818348
    2x (C7,8) 100 µF 16V electrolytic capacitor http://www.digikey.com/product-detai...601-ND/3083016
    1x (C11) 100 µF 35V electrolytic capacitor http://www.digikey.com/product-detai...104-ND/2712510
    2x (D1,2) 1N914 diode http://www.digikey.com/product-detai...ACT-ND/1626125
    1x (D3) 1N5359B zener diode 24V 5W http://www.digikey.com/product-detai...GOS-ND/1474107
    1x (LS1) loudspeaker 8 ohm http://www.digikey.com/product-detai...268-ND/1745562
    1x (MIC1) electret microphone http://www.digikey.com/product-detai...723-ND/1869983
    2x (Q1,3) BC337-25 transistor http://www.digikey.com/product-detai...GOS-ND/1475621
    2x (Q2,4) BC327-25 transistor http://www.digikey.com/product-detai...GOS-ND/1475586
    1x (R1) 5k6 resistor http://www.digikey.com/product-detai...ACT-ND/2617520
    2x (R2,8) 100k resistor http://www.digikey.com/product-detai...KCT-ND/1975158
    3x (R3,7,9) 22k resistor http://www.digikey.com/product-detai...ACT-ND/2617471
    1x (R4) 10k resistor http://www.digikey.com/product-detai...ACT-ND/2617809
    1x (R5) 2k7 resistor http://www.digikey.com/product-detai...ACT-ND/2617483
    1x (R6) 200R trimpot http://www.digikey.com/product-detai...1LF-ND/1088415
    1x (R10) 100k trimpot http://www.digikey.com/product-detai...4LF-ND/1088413
    1x (R11) 5k trimpot http://www.digikey.com/product-detail/en/3362P-1-102LF/3362P-502LF-ND
    1x (R12) 33R 3W resistor http://www.digikey.com/product-detai...4CT-ND/3477464
    1x (R13) V18ZA40 varistor http://www.digikey.com/product-detai...078-ND/1009327
    1x (U1) CD4093B integrated circuit http://www.digikey.com/product-detai...068-5-ND/67329
    1x 14-pin DIP IC socket for U1 http://www.digikey.com/product-detai...205-ND/1125623
    1x (U2) µA7809, LM7809 etc three-terminal regulator http://www.digikey.com/product-detai...GOS-ND/1481254
    stripboard (aka veroboard) see https://en.wikipedia.org/wiki/Stripboard
     

    Attached Files:

  20. decetch

    decetch

    8
    1
    Sep 2, 2013
    Hi Everyone,

    At long last I'm able to report that I had someone build the parking sensor circuit designed by KrisBlueNZ and that it was fitted today by my Toyota dealer. The fitting of this box of tricks in no way voids warranties etc as it is a stand alone circuit. The person who built if for me included two dials (you can tell I'm not very electronics orientated) one for volume and one for tone/pitch. They were mounted on the plate next to the blind spot monitor. But even better, it works like a charm. At last I'm able to hear the parking sensors. So Kris, thank you very much for the trouble you went to, I really appreciate it. Thanks also to all the other members who contributed to this thread. I'm a happy man.

    Decetch
     
    KrisBlueNZ likes this.
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