Timeline for Why does controlling power with a transistor interfere with MHZ19B's serial communication?
Current License: CC BY-SA 4.0
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| Jun 17, 2023 at 21:05 | history | bumped | CommunityBot | This question has answers that may be good or bad; the system has marked it active so that they can be reviewed. | |
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| Sep 30, 2020 at 15:25 | answer | added | starship15 | timeline score: 1 | |
| Sep 29, 2020 at 20:14 | comment | added | Wirewrap | @Gerben R2 is okay. The base of Q1 will not go more than one diode drop below 5V regardless of R2 value. | |
| Sep 28, 2020 at 21:52 | answer | added | Gil | timeline score: 1 | |
| Sep 28, 2020 at 21:04 | history | edited | Constantin | CC BY-SA 4.0 | edited title |
| Sep 28, 2020 at 18:55 | comment | added | Gerben | It seems software serial doesn't have a function to "disconnect". A workaround is to set the TX pin to an INPUT, and to LOW (pinmode(txPin, INPUT); digitalWrite(txPin, LOW);). Then make sure you don't call any mySerial.print commands while power is off. Then when powering on the chip, do the reverse (pinmode(txPin, OUTPUT); digitalWrite(txPin, HIGH); | |
| Sep 28, 2020 at 18:47 | history | edited | Constantin | CC BY-SA 4.0 | added 31 characters in body |
| Sep 28, 2020 at 18:46 | comment | added | Gerben | PS R2 looks weird to me. I think you need to move it the the horizontal section. Otherwise you only get 2.5V at the base of Q1, when Q2 is turned on. | |
| Sep 28, 2020 at 18:44 | comment | added | Gerben | You need to disconnect the serial, before turn of the power of the module. What I think happens is that the TX pin on MCU (RX on the MHZ19b) is HIGH when it isn't sending it anything. So you get 3.3-5V going into the MHZ19b that's powered down (which is bad). A lot of chips have clamping diodes on there input pins. So you are essentially powering the chip via the TX pin. The TX pin can supply enough power to the chip, with cause weird things to happen. For example gibberish UART data. | |
| Sep 28, 2020 at 18:39 | history | edited | Constantin | CC BY-SA 4.0 | added 39 characters in body |
| Sep 28, 2020 at 18:25 | review | First posts | |||
| Oct 4, 2020 at 7:56 | |||||
| Sep 28, 2020 at 18:22 | history | asked | Constantin | CC BY-SA 4.0 |