Mini Fog Machine / PT2272 RF Module Issue - Page 1
Forum section: electronics / beginners

author: Qgel
author_rank: Newbie
timestamp: February 21, 2019, 01:41:54 pm
content: Hello,I'm currently experiencing an issue with a circuit which should be very simple, but is behaving strangely. What I am trying to build is the attached schematic. Basically, I'm trying to switch a load on/off using an RF receiver module. The load in this case is basically just a resistor of 2 ohm (e-cigarette vaporizer for a miniature fog machine).Expected behavior:When the button on a remote is pressed, the DATA pin on the RF module will go high. This will open the channel on the MOSFET and turn on the load. When the button is released, the DATA pin goes low and the load is switched off.Actual Behavior:The load will turn on/off with a frequency of approximately 4-5 Hz.Where it gets weird:If i disconnect the DATA pin and drive the MOSFET Gate directly with a bridge to VCC, the load turns on and stays on as expected. While the load is on, the DATA pin on the RF module is always 0 (measured with a multimeter). I.e. even though in this configuration the DATA pin is not connected to anything, and the only connections of the RF Module are the VCC and GND connections, it ceases to work.What I've tested:Measured the voltage between RF Module VCC and GND with/without the load on. Without load it was 4.1V, with load it dropped to 4V. I tested the RF Module in isolation at 3.7V and it works without problemsDisconnected the load. In this case the RF Module seems to be able to switch the MOSFET without problems. At least, the voltage at DATA behaves as expectedUsed a different load (DC Motor). The same issue occursUsed a different MOSFET (IRLB8721). The same issue occursUsed a different LIPO without short protectionAdded a 220uF cap between VCC and GND at the RF ModuleAt this point I'm running out of ideas what the problem might be. Maybe something causes noise on VCC which I cannot see with the multimeter or something interferes with the 315 Mhz RF signals? I might get access to an oscilloscope this evening, so I can at least look at VCC voltage with/without load on.Any help would be greatly appreciated.The components are:Simple RF M4 Receiver:https://www.adafruit.com/product/1096IRLB3034 MOSFET:https://www.infineon.com/dgdl/irlb3034pbf.pdf?fileId=5546d462533600a40153566027b22585Power Source 2000mAh 3.7V Lipo:https://www.adafruit.com/product/2011

author: mroek
author_rank: Contributor
timestamp: February 22, 2019, 09:47:41 am
content: You are probably operating at or below the supply voltage limit for the RF module. Powering it from a 3.7 V LiPo isn't the best idea when the datasheet says it needs 4-15 V. Yes, the LiPo outputs a little over 4 V at full charge, but it is still a bad idea (even if you were able to get the module to appear to work in isolation at 3.7 V).You are probably getting some kind of oscillation due to the voltage drop when the load is switched on, but you need a scope to properly see what's happening. But no matter what, you should try supplying the RF module with the proper voltage. As a simple test, why don't you try supplying the RF module with 5 V separately and see if it works in that configuration?

author: Qgel
author_rank: Newbie
timestamp: February 22, 2019, 11:34:27 am
content: I tried running everything from a lab power supply yesterday and experienced the same issues. Started testing at 4.5V and went up to 6V.With everything connected, the current draw was about 2.5A. With just the DC Motor connected it was about 0.3A.I also used an oscilloscope yesterday to look at the voltage between VCC and GND, but I'm not sure of what to make of it. When the load is not engaged, the Lab power supply was clean at 5V. With the load engaged, it looked like the picture below. Notice the faint yellow waveform around the set voltage, which was only visible when the load was engaged. Not sure what to think of this, but really I don't have an idea what I'm doing/looking for here. Note that this test was done with the mosfet switched on 'manually', i.e. not by the RF module.During testing yesterday I seem to have destroyed the RF Module (probably shorted something on my messy workbench), so it's hard for me to do more tests currently. I'm still looking for ideas of what the issue might be though, so I can get a new RF Module and get this thing running still.

author: jackthomson41
author_rank: Regular Contributor
timestamp: February 22, 2019, 02:05:19 pm
content: Add capacitor between Vcc & GND, it may be because of noise etc. Try this rf modulePT2272with somemicrocontrollerlikeArduino UNO,Arduino Pro Minietc.

author: Qgel
author_rank: Newbie
timestamp: February 25, 2019, 04:02:37 pm
content: Quote from: jackthomson41 on February 22, 2019, 02:05:19 pmI already tried a quite big capacitor, see above. I'm not sure how exactly I would test the RF Module with an Arduino. As I said, it works fine in isolation.