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I'm using an Arduino to realize two "simple" tasks. The Arduino shall receive messages by an 433MHz receiver and send them via ESP8266/ESP-01 to a server. The schematic/wiring plan is attached below.

As you will see, there is a connection between ESP8266's and Arduino's GND. This ist necessary, because otherwise I couldn't get a proper serial connection between them both.

But this connection also "kills" the functionalty of my 433MHz receiver. Once the grounds are linked, I get a "noise" on the 433MHz receiver's data line.

I watched the receivers data line with the poor man's oscilloscope and could see that the receiver starts to output strange signals when the grounds are linked together. I also hooked up the Arduino 5V line on oscilloscope and could that once the grounds are linked, the 5V line isn't "stable" any longer. (It drops one ore more times per seconds from 5V to ~4.7V).

What am I doing wrong? How can I get a proper serial connection between Arduino and ESP8266 without "disturbing" my 433Mhz receiver?

enter image description here

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    \$\begingroup\$ Why are you using multiple power sources? And why are you putting 5V into the Arduino's barrel socket? \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 16 '15 at 6:28
  • \$\begingroup\$ I'm using multiple power sources, because ESP8266 needs up to 300ma on peaks and the Arduino's circuit can draw a maxium of 200ma (playground.arduino.cc/Main/ArduinoPinCurrentLimitations). The 5V to barrel, was wrong in schematic. I fixed the image in my initial post. \$\endgroup\$ – netblognet Feb 16 '15 at 6:32
  • \$\begingroup\$ Arduino won't draw that much, it is a maximum. IIRC UNO uses about 40mA \$\endgroup\$ – geometrikal Feb 16 '15 at 6:34
  • \$\begingroup\$ @geometrikal For that reason I added a second power supply. To be clear, both, the 433Mhz on Arduino and the ESP8266 on it's board run fine and have enough power. But to let them "talk together" by serial connection (via Pin 10,11 / SoftSerial) I have to "link their" grounds. From that moment on, the 433Mhz produces gibberish/crappy data signal. So the questions are: How can I get a serial connection without linking their grounds? (or) How to avoid the voltage drops on Arduinos circuit when linking grounds. \$\endgroup\$ – netblognet Feb 16 '15 at 7:00
  • \$\begingroup\$ 200mA is the maximum the Arduino MCU can supply. As in you can't have things connected to the pins that draw more than 200mA total. You should use a single power supply and connect both the Arduino and breakout to it. Sometimes connecting grounds of multiple switchmode power supplies can cause problems. \$\endgroup\$ – geometrikal Feb 16 '15 at 7:31
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The ESP8266 draws between 40ma and 80mA when connected to a Wifi network but can peak up to around 200mA when transmitting. This sudden drain on the power can cause a voltage drop that may trigger a reset of other devices in the circuit. You should add a large capacitor close to the ESP8266 module. I've used 10uF successfully but you might need more. I would suggest you add one for the 433Mhz module as well.

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    \$\begingroup\$ If the duration of these peaks are really small, I would also add a 100nF or 10nF ceramic capacitor along with the 10uF. This is to supress the high frequency switching noise. \$\endgroup\$ – Golaž Feb 16 '15 at 11:34
  • \$\begingroup\$ I added capacitors and now the Arduino's 5V line doesn't drop any longer! Thanks therefore. Unfortunately the main problem isn't gone. Even if the voltage doesn't drop the data line of the 433Mhz receiver is manipulated by the ESP-board. For clearance have a look at the following screenshot, which shows the dataline: fs2.directupload.net/images/150217/im7swcmm.png \$\endgroup\$ – netblognet Feb 17 '15 at 18:18
  • \$\begingroup\$ How can this be the cause if they are on separate power supplies? \$\endgroup\$ – marcelm Jan 14 '17 at 18:34
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I am struggling with the same problem.. I can offer a workaround though: I am using an 5V boost converter before the arduino and the RF module on the 5V power line. http://www.ebay.com/itm/5PCS-PFM-Control-DC-DC-USB-0-9V-5V-to-5V-dc-Boost-Step-up-Power-Supply-Module-/201197341104?pt=LH_DefaultDomain_0&hash=item2ed84bc9b0 So the input of the boost converter is actually 5V but it somehow manage to filter the power line so the RF module can receive data again with connected wifi module. I am still looking for a better solution, I tried to add different type of capacitors in paralell on different places but nothing helped... maybe the coil on this little dc-dc booster is the solution? Or the power regulator on it? I really don't know. Any further help would be greatly appreciated.

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  • \$\begingroup\$ Welcome to EE.SE. Are you trying to ask a new question? If so, please post it as a new question rather than as an answer to a previous question. \$\endgroup\$ – Null Jul 4 '15 at 2:48
  • \$\begingroup\$ Hi, thanks for the comment! Actually I offered a solution for the original question (How can I get a proper serial connection..) and I am still looking for an other solution, so my question is still the same as the original poster. I really want to know what I should do with this setup to make it work without the 5V booster. Maybe adding capacitor or a coil? I can feel the real solution is close and I don't want to discuss it an another thread because my opinion is that these things are strictly connected. \$\endgroup\$ – gOldie_E36 Jul 4 '15 at 7:16
  • \$\begingroup\$ Understood. I do not have a different question :) Keep waiting for other answers/solutions for the original one: "How can I get a proper serial connection between Arduino and ESP8266 without "disturbing" my 433Mhz receiver?" \$\endgroup\$ – gOldie_E36 Jul 4 '15 at 15:37

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