Shop OBEX P1 Docs P2 Docs Learn Events
rs232 volage into stamp pin... — Parallax Forums

rs232 volage into stamp pin...

FORDFORD Posts: 221
edited 2006-06-01 22:41 in BASIC Stamp
Hi all,
I would like to hook the DTR from a serial printer straight to a stamp input.
Would something like a 10K resistor be OK to protect the stamp input ?

Cheers,
Chris
West Oz.

Comments

  • BeanBean Posts: 8,129
    edited 2006-06-01 13:05
    Yep, I usually use a 22K just to be safe.

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Cheap 4-digit LED display with driver IC·www.hc4led.com


    COMING SOON "SD DATA LOGGER" www.sddatalogger.com

    "I reject your reality, and substitute my own." Mythbusters
    ·
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-06-01 13:26
    22K is needed.

    What happens is, the +- 12 volt signal can be 'clipped' internally with the PIC16C57 'protection diodes' on each pin. However, these 'protection diodes' can only handle so much current. So, the 22 Kohm resistor reduces the amount of current so the protection diode can 'clip' the signal without damage to the diodes.

    The current is (using V = I*R) : (+12 - 5) / 22e3 == 0.318 mA

    (-12 + 0.3) / 22e3 == 0.531 mA

    You'd have to look at the data sheet on the PIC to see how much current the protection diodes can handle. Less than 1 mA shouldn't be a problem, though.
  • FORDFORD Posts: 221
    edited 2006-06-01 22:41
    thankyou for the information, i'll go with 22k.

    cheers, chris
Sign In or Register to comment.