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| MAX485, ok with 2 nodes, when 3rd node powered up voltage drop below 2V (SOLVED) |
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| stan001:
Hi, I made a MAX485 module with the schematics below... Everything was working OK when 2 nodes were connected, can Rx or Tx between the master/slave nodes on the Arduino Nano. - I have tried using 20K pull-up/down at A,B or even no pull-up/down on A,B, same results. - I tried with 120R termination or 1K R termination, same results. - Was running at the lowest speed of 9600, same results. I'm using just very short Cat 5E twisted pair cables during the tests.. I can visually see it is not working as the Rx,Tx LED becomes very dim or not litted at all.. Any idea why does it drop the voltages when 3 or 4th nodes was connected ?? Thank you for reading this.. MAX485-sch When running on 2 nodes, everything was ok. MAX485-2nodes When connected n power up the 3rd node, voltages dropped below 2V MAX485-3nodes Here is a picture of my setup with the newly made PCB.. MAX485-Eduboard |
| capt bullshot:
You have placed a pull-up resistor (R2) on the control input. This puts the output of the MAX485 into active state (transmitting) when nothing is connected. So now you have a transceiver transmitting a static level against your data lines, resulting in the reduced signal level. Change that resistor to a pull-down resistor and it should work. |
| stan001:
Thanks a lot, you are spot on.. i removed the 10K pullup and let the Arduino pins control the HIGH/LOW state.. |
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