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Voltage on UART pins

SailCS33

SailCS33

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Feb 16, 2020
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I just received JBD SP04S034-H BMS. The seller forgot to include the BT module. While I am waiting for them to send it, I wanted to connect UART to my laptop over USB. I am getting 13.3 volts on pin 4. Is it normal? I am afraid of trying UART USB with my laptop.
 
IMHO, you won't need to use the VDD pin on the UART. Normally just the Tx and Rx pins with respect to ground is needed.

But, as @kommando mentioned, you will need to galvanically isolate the BMS from the laptop's ground. With my (overkill badged) JBD I purchased a JBD UART to USB adaptor for that purpose - this one:-

USB Module for BMS – Overkill Solar

overkillsolar.com overkillsolar.com
 
Thank you, you right I should not need this pin to connect to the laptop. Do you happen to know if this voltage will become a problem when Jbd sends me the BT module they forgot initially?
 
SailCS33 said:
Do you happen to know if this voltage will become a problem when Jbd sends me the BT module they forgot initially?
Click to expand...
I don't, but would assume it is designed to work together correctly :unsure:. The spec mentions that pin is VDD, which I would normally expect to be +5V, rather than 12V. May be worth checking with your supplier what input voltage the BT adapter is expecting.

Maybe others on here have a JBD working with the BT adapter and could check?
 
The minimum and maximum voltages of a true RS232 signals are +/- 12/13V., while TTL signals are 0 to 3,3V/5V. The differences between a TTL RS232 (also called RS232-C) and a True RS232 interface is only related to the signal level to GND (Ground) and not with the current to power the device

electronics.stackexchange.com

What is the difference between RS-232 and TTL UART?

I always need to communicate with the TTL UART port on the MCU with a computer. When I talked about that, people always refer the UART port as an RS-232 port. Are they correct? If not, what is the
electronics.stackexchange.com electronics.stackexchange.com

www.seeedstudio.com

RS232 vs TTL: Beginner Guide to Serial Communication - Latest Open Tech From Seeed

Serial communication is a way for data transmission over long distances. Commonly associated with RS232 and TTL serial, it enables Arduino and other microcontrollers to communicate with your computer or other serial devices.
www.seeedstudio.com www.seeedstudio.com
 
I believe UART and RS232 are not interchangeable terms. UART is an interface while RS232 is a protocol/standard. RS232 communication can be using UART interface but does not have to (in theory). This geeky stuff is over my pay grade but from what I read, the signal that follows RS232 standard "can" be as 3v-15v +/-
 
Just received the answer from JBD. Their engineering confirmed pin 4 on UART is equal to battery positive to power their BT module.

So I guess to you any generic BT module one would have to step it down to 5v
 
SailCS33 said:
Just received the answer from JBD. Their engineering confirmed pin 4 on UART is equal to battery positive to power their BT module.

So I guess to you any generic BT module one would have to step it down to 5v
Click to expand...
Result! (y) guess that will mean my 16s BMS will be 50V+ then!
 
SailCS33 said:
well thats a great question. Here is a screenshot of what I received for what it's worth.

View attachment 209620
Click to expand...
The next question is if they even make a 4 series 16s BMS, and if the Vdd pin would be something else in that scenario, or if their 4 series BT module can handle 60V.

This is of course, in addition to the question of why they make a high voltage and a low-voltage Bluetooth interface with the same connector. I mean, who would’ve ever imagined someone would plug the wrong thing in?
 
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