Drop in the voltage

gablor

I developed a PC application that sends character· through a serial connection.· I cut the serial wire and tap the DT and Common and test the voltage accross using the parallax oscilloscope.· The initial result is as shown in before_connection.jpg.· I·connected the DT wire to a 22 ohms resistror and then connected the other end of the resistor to·P5 of the parallax BOE·board. I also connected the COMM to the VSS.· I measured the two wires again at the point where they are·connected to the BOE board.· The result is as·shown in after_connection.jpg.··Can anyone explain to me why there is a voltage drop?· I am not an electrical engineer and just wanted·my·PC to control motors using the BOE board(BS2 micro controller).··Can anyone help me make this connection work?·Any suggestion?·

gablor

I found the reason. When I took the measurement after connecting to the BOE board I forgot to power up. When I turn on the power it generated the right voltage.

JD

Gablor,

·Excellent. I have to say thank you for posting that you found the solution; that helps the others on the forums not look for an answer that has already been answered.

How is the PC control coming along?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Respectfully,


Joshua Donelson
www.parallax.com

gablor

It is working now. It's a bit of a learn as you go process. After I made the connection work I found out I am getting inverted signal. After some fixing I was able to get the right bit sequence (the exact character I sent from the PC). Here's how I coded it:


#SELECT $STAMP
#CASE BS2, BS2E, BS2PE
T1200 CON 813
T2400 CON 396
T9600 CON 84
#CASE ...
#ENDSELECT
Inverted CON $4000
Baud CON T9600 + Inverted ' to get the right order bit sequence - for
letter VAR Byte

SERIN SI\FC, Baud, [noparse][[/noparse]letter] ' to get the character sent by PC


I am coding to link my HB-25 to the STAMP to operate the higher AMP motor I will use. I Will send a video later when it's running.