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Regulating a 12v DC Power Source - Page 3 — Parallax Forums

Regulating a 12v DC Power Source

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  • willthiswork89willthiswork89 Posts: 359
    edited 2006-09-14 16:31
    alright here is my first attempt in using this, i did not see your post till i was finished so tell me what you think anyways.



    Paul,

    the Wiring schematic is fairly striahgt forward i have a 5 wire digital clock in my car, Not positive on the wiring but i know there is positive and ground heh, i figured out that they have 12 volts when the car is starting also so i went ahead and used this for a power source because it powers up when i have the key in Pos II or III so its fairly simple! im actually going to get pictures since they didnt save i wish they would of but it doesnt take long to take he car apart haha. But i think that the power supply will differ from car to car, since most cars have different wiring mine is only good for the honda prelude. you would have to get a chiltons book on your car, it says HOT WHEN ON OR STARTING, anything with that saying you can use that wire to tap the power from! hope this helps. more to come

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    -Learn somthing about everything, and Everthing about somthing-
  • Beau SchwabeBeau Schwabe Posts: 6,559
    edited 2006-09-14 20:33
    willthiswork89,
    ·
    There are a few things that you must consider and make part of your design practice in future designs as well as this one·if you want·your projects·to last...
    ·
    ·
    1) Any inductive load ... a relay, motor, etc. needs to have a diode in a reverse biased fashion across it.·
    ··· I have added this to your·schematic as D3
    ·
    2) Because you have an automotive application, You should apply this same thinking as if the entire 12V electrical system·of the car is an inductive load... because it IS.·
    ··· I added D4 to the schematic
    ·
    3) Because automotive electrical systems are notoriously noisy (electrically) you should also have some filtering on the front end of your regulators.·
    ··· I added C3 and C4.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
    986 x 427 - 50K
  • willthiswork89willthiswork89 Posts: 359
    edited 2006-09-14 22:08
    wow, thanks Beau, see i knew they were very noisy and i mentioned that somwhere in this string and i though that the C1 and C2 were solving that, i do not know what inductive loads are so i will look that up, from the examples it means anything that will cause a back EMF from when the electricity stops. correct me if im wrong. So what is D4 doing for me? wont that short the system out because on the other end is a +12 volts? im sure that it is correct but im still pretty new and i understand basics but that is stuff i havnt learned about.

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  • willthiswork89willthiswork89 Posts: 359
    edited 2006-09-14 22:56
    Alright guys, i have until monday to figure out the most compact way to put these things, keep in mind that my regulators(both of them) have heat sinks on them. i bought a solder bread board with 5 connecting holes on one side and 5 connecting holes on the other, 45 rows of 5 * 2 lol so im trying to make this as neat and compact as i can, if any of you guys that have the compact skill haha, i could try 3 days what would take some of you 5 minutes to organize everything! so if someone possibly has skills in eagle and can make a PCB or even a schematic with everything fit as tight as possible on a breadboard i would appreciate it!

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  • willthiswork89willthiswork89 Posts: 359
    edited 2006-09-20 10:46
    Alright guys i got the circuit board done and ive played quite a bit with the rfid reader i think im pretty comfertable, if comeone could please check m code im appreciate it so i can make some ajustments and get this running as smooth as possible! im going to be installing it in the car here today or maybe ill wait till this weekend. havnt decided yet!

    ' =========================================================================
    '
    '·· File...... CarSecurity.bs2
    '·· Purpose... ToDisable Car Starter
    '·· Author.... Kevin Stowe
    '·· E-mail.... willthiswork89@msn.com
    '·· Started...
    '·· Updated...
    '
    '·· {$STAMP BS2}
    '·· {$PBASIC 2.5}
    '
    ' =========================================================================

    '
    [noparse][[/noparse] Program Description ]
    ' This Program is to Operate and Disable the Starter for a car

    '
    [noparse][[/noparse] Revision History ]
    ' Version 1.0 Using a Push Button
    '
    [noparse][[/noparse] I/O Definitions ]
    RFIDEnable··· PIN 0······· 'Enable RFID Reading PIN
    RFIDRX······· PIN 1······· 'SERIN PORT FOR RFID
    Relay········ PIN 15······ '20Ma Reed Relay SPST
    StarterLight· PIN 14······ 'Light to Tell me good swipe, start car
    BadSwipe····· PIN 13······ 'Light to tell me bad swipe, do it again

    '
    [noparse][[/noparse] Constants ]
    YesRead······ CON 0······· 'Begin Read(Low)
    NoRead······· CON 1······· 'End Read(High)
    Enable······· CON 1······· 'On(High)
    Disable······ CON 0······· 'Off(Low)
    Time········· CON 30000··· 'Ammount of time alloted to start car
    Baud········· CON 396····· 'Baud Rate from RFID SERIN Command

    '
    [noparse][[/noparse] Variables ]
    Swipe········ VAR· Byte(10) 'Array for Incomming Swiped Card
    IDX·········· VAR· Byte···· 'Index Variable for going through Swipe
    Character···· VAR· Byte···· 'Character Byte for reading and comparing EEPROM Data
    DebugMode···· VAR· Bit····· 'Enable Debug Mode

    '
    [noparse][[/noparse] EEPROM Data ]
    DATA "04158DB92F"·········· 'My RFID Card EEPROM Data
    '
    [noparse][[/noparse] Initialization ]
    OUTPUT Relay
    OUTPUT RfidEnable
    OUTPUT StarterLight
    OUTPUT BadSwipe
    Reset:
    RFIDEnable = NoRead

    '
    [noparse][[/noparse] Program Code ]
    Main:
    GOSUB BeginRead
    DEBUG "Going to Checkread"
    GOSUB CheckRead
    DEBUG "Completed Car Started Successfully!"
    END

    '
    [noparse][[/noparse] Subroutines ]
    BeginRead:
    RFIDEnable = YesRead
    SERIN RFIDRX, Baud, [noparse][[/noparse]WAIT($0A), STR Swipe\10]
    RFIDEnable = NoRead
    RETURN
    CheckRead:
    FOR IDX = 0 TO 9
    READ(IDX),Character
    IF(Swipe(IDX) <> Character) THEN
    Badswipe = Enable
    PAUSE 500
    Badswipe = Disable
    PAUSE 500
    DEBUG "Bad Swipe"
    GOSUB Reset
    ENDIF
    NEXT
    StarterLight = Enable
    Relay = Enable
    PAUSE Time
    StarterLight = Disable
    Relay = Disable
    RETURN

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  • willthiswork89willthiswork89 Posts: 359
    edited 2006-09-21 23:35
    alright guys before i hook it up in order to take advantage of the stamps 5 volt regulator too, should i hook it into VSS or VIN? i dont wanna blow the stamp up or anythng so can someone simply answer that for me and will it mess anything up on the RFID reader to be on constantly? even when the stamp goes into low power mode ive noticed that the RFID reader remains lit up bright green so will it ruin or anything?

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    Post Edited (willthiswork89) : 9/21/2006 11:46:47 PM GMT
  • willthiswork89willthiswork89 Posts: 359
    edited 2006-09-26 10:46
    alright well so far no one has answered any of my questions to problems im facing but hopefully someone can answer this one.... the reader and my program were working fine but would about 9-12 feet of wire spread from the RFID reader to the stamp make a difference in whats going on? its acting up and flashing the RED to GREEN and wont read anything. If anyone knows what it might be please tell me if thats not the case! im going to go ahead and debug to make sure its not my program.

    Bad Solder Joint, it broke off the breadboard line and i didnt notice, that was causing the no read and it was touching the enable which was causing it to flash.

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    Post Edited (willthiswork89) : 9/26/2006 11:26:54 AM GMT
  • Mike GreenMike Green Posts: 23,101
    edited 2006-09-26 14:23
    The general rule for connecting anything "off board" is that it depends on the environment, the distance, and the speed. For example, if you're trying to connect over a distance of 10-12 feet in an electrically quiet environment (where you're not running wires in parallel with other wires with a lot of electrical noise - like in a car's wiring harnesses) and your voltage levels are 0 and 5V and the highest speed is 9600 Baud, it will probably work. Twisted pair wires will help (and may be all you need). Shielded wires with the shield connected to ground (at one end only - to avoid ground loops) will help if there's a lot of electrical noise. Over longer distances (100s to 1000s of feet) or higher speeds (50-100 kBaud) you will need RS232 or RS423 driver/receiver chips and shielded twisted pair wires to get reliable communication.
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