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Free Pins on Proto Board — Parallax Forums

Free Pins on Proto Board

RaymanRayman Posts: 14,791
edited 2007-10-20 16:34 in Propeller 1
I was just counting the free pins on the Proto board (assuming I'm using VGA, mouse, and keyboard) and got 20, with 12 in use.·

But, one thing I don't understand is the markings on the schematic (http://www.parallax.com/dl/docs/prod/prop/Propeller-ProtoBoard-v1.1.pdf) for pins P24-P27.· They seem to indicate that these pins might be normally used for something, but I don't see what...

Anybody know?· I see they are hidden behind the crystal.· Maybe this is all they mean?· But, why the different symbols on each one?

Comments

  • NewzedNewzed Posts: 2,503
    edited 2007-10-19 13:14
    Pins 24-27 are used for the mouse and keyboard.

    Sid

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    Yesterday is history, tomorrow is a mystery, and today is a gift.

    That is why they call it the present.

    Don't have VGA?
    Newzed@aol.com
    ·
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2007-10-19 13:25
    Yes those pins are routed to the part of the protoboard where the VGA/mouse/keyboard connector block resides, unless the resistors are added then they are not connected to the actual connectors and you can use the pins for anything.

    Graham
  • RaymanRayman Posts: 14,791
    edited 2007-10-19 13:52
    Ok, I need some coffee!
  • RaymanRayman Posts: 14,791
    edited 2007-10-19 13:59
    So, I guess I'll have 16 free with 16 in use...
  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-19 15:09
    If you need expansion, the PCA9554 from Philips is a nice 8-bit I2C bidirectional I/O expander that can be hooked up (up to 8 of them) on pins 28/29. BoeBotBasic uses this for access to an HB55 compass and the same I2C routines used there for access to the EEPROM are used for the PCA9554. It'll run on 3.3V and has 5V tolerant I/O pins.
  • RaymanRayman Posts: 14,791
    edited 2007-10-19 18:07
    Thanks Mike: "5V tolerant I/O pins" is very interesting to me because I want to drive 5V relays...
  • deSilvadeSilva Posts: 2,967
    edited 2007-10-19 18:12
    Alas, "5V tolerant" refers to input smile.gif
  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-19 18:28
    Rayman,
    You'll still need an MOSFET or small switching junction transistor to drive the relay. Neither the Propeller nor the PCA9554 have enough current drive for most relays. There is one reed relay from US Relays that I found in the Digikey catalog that will work directly off a Propeller I/O pin. It's rated for a 3V input and the current required is about 20ma. Their stock number is Z622-ND and the manufacturer's number is R1A3AHH. All you need is a diode reverse connected across the coil (like a 1N4001).
  • RaymanRayman Posts: 14,791
    edited 2007-10-19 21:34
    Well, I just wanted to sink some current to drive the relay... But, the chip would see 5V when the output was high impedance... I was planning on using a i2c level shifter, but I'll have to take a closer look to see if I can get away without it...

    I just checked and I need 40 mA to drive the relay...· Still, if I bussed·a few·outputs together, it might work...

    Post Edited (Rayman) : 10/19/2007 9:43:19 PM GMT
  • RaymanRayman Posts: 14,791
    edited 2007-10-19 21:55
    This looks like a pretty good combo here: http://www.avrcard.com/products/octal_out.htm

    Can sink 500 mA with OC output that can handle up to 50 V. I already have a PCF8574, which looks a lot like the PCA9554...
  • SapiehaSapieha Posts: 2,964
    edited 2007-10-19 21:59
    Hi Rayman.

    You can use 74ls06 to drive 40mA relay

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Nothing is impossible, there are only different degrees of difficulty.

    Sapieha
  • RaymanRayman Posts: 14,791
    edited 2007-10-20 00:20
    The 74ls06 is also an open-collector output, but it is just hex... The PCF8574 and ULN2803 are both octal...
  • Ken PetersonKen Peterson Posts: 806
    edited 2007-10-20 03:08
    Mike,

    Thanks for mentioning the PCA9554. I think that will be a nice one to have in my back pocket if I ever paint myself into a corner and need extra pins. A colleague of mine would have found this one useful on his project because he ran out of pins. He ended up doing something different, but the software ended up being somewhat ugly.

    Seems like once you are done, you see a better way of doing it. That's one of the hard realities of being an engineer.

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    The more I know, the more I know I don't know.· Is this what they call Wisdom?

    Post Edited (Ken Peterson) : 10/20/2007 3:18:11 AM GMT
  • RaymanRayman Posts: 14,791
    edited 2007-10-20 12:22
    I just found this thing that will let me drive a 5 V relay from 3.3 V cmos logic:

    MDC3105

    It's only in single and dual packages and only in SOT23 package. But, I think it will make things much simpler for me...
  • Ken PetersonKen Peterson Posts: 806
    edited 2007-10-20 13:34
    the MDC3105 is basically a transistor and a few added components on a chip. You should be able to do the job with one transistor, one resistor, and one diode (for the coil spike), and only one prop pin.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


    The more I know, the more I know I don't know.· Is this what they call Wisdom?
  • RaymanRayman Posts: 14,791
    edited 2007-10-20 13:53
    True. But the app I'm working on needs more pins. So, I want to use i2c i/o expanders...

    But, on second thought, I need to drive at least 4, and maybe 10 or more relays. So, I think I'll level shift the I2C bus to 5 V with a PCA9512 and then use a PCF8574 (or PCA9554) with ULN2803 to control up to 500 mA relays.
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2007-10-20 13:54
    If you do have lots of relays to drive there are some nice darlington arrays out there.

    Graham
  • RaymanRayman Posts: 14,791
    edited 2007-10-20 15:40
    The ULN2803 is an octal darlington array with built in free-wheeling diodes...
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2007-10-20 16:06
    Notice the time of your last post and mine, I was reading the datasheet and replying when you replied [noparse]:)[/noparse]
  • RaymanRayman Posts: 14,791
    edited 2007-10-20 16:30
    That happens to me a lot!
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2007-10-20 16:34
    p.s. I bet that happens to you a lot too



    p.p.s [noparse];)[/noparse]
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