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connecting serial directly from TT4 board?

 

My preferred setup is to combine the TT4 with a Raspberry Pi Zero W.? I have been using the TT4BT to provide serial to the Pi, but is there a place on the board I can easily? connect J2 pins 2&3 serial direct??

This would? cut the power consumed by 50ma and be a more reliable connection.

Thanks
 

The issue with connecting directly to the Pi is that the Pi uses 3.3V TTL serial communication and the TT4 uses standard RS-232 (which is +/-5V minumum).?? With the kit version, either or both ports (A & B) can be set to TTL serial, and with the preBuilt PortB can be set to TTL serial.? BUT ...?? the TT4 is 5V logic, while the Pi is 3.3V logic.

Options:
1. Obvously you can use a Micro-USB to RS232 adaptor, but the really isn't a direct connection
??? No change in jumpers required.
2. Set TT4 JP7 for TTL on connected port and use the Pi pins 8 & 10 (3.3V logic serial) to pins 2 & 3? of J2 with resistors of the TT4.
??? Proper method would be 2 resistor voltage divider to drop the 5V to ~3.3V to the Pi RX pin (10).? Works at 19,200 baud.
??????? Resistors of TT4 2200 ohms to Pi and from there 4300 ohms to ground works well.
??? Some users will use a single resistor in the Pi RX pin (10)? to limit current.? I know lots of people that do this.
??? The 3.3V will be enough to toggle the TX pin of the TT4 so nothing needed there.
3. Use another MAX232 (not the correct part as this is 5V to RS232) chip to level shift the Pi to the TT4
??? No change in jumpers required.
4. Us a 3.3V to 5V level shifter (some are made for I2C).?
??? I have not tried this, but if it works for I2C, it should work for TTL serial.
??? Set TT4 JP7 for TTL on connected port.?

So your direct answer is, not without a few added parts/

Robert Giuliano
KB8RCO



On Friday, April 2, 2021, 4:07:02 PM EDT, Peter VE7PPE <ve7ppe@...> wrote:


My preferred setup is to combine the TT4 with a Raspberry Pi Zero W.? I have been using the TT4BT to provide serial to the Pi, but is there a place on the board I can easily? connect J2 pins 2&3 serial direct??

This would? cut the power consumed by 50ma and be a more reliable connection.

Thanks

 

Adafruit sells a nifty 3.3v to 5v converter board for exactly this situation. 2, 4, and 8 signal versions available



Cliff k6cls cm87




On April 2, 2021 6:11:23 PM PDT, "Rob Giuliano via groups.io" <kb8rco@...> wrote:
The issue with connecting directly to the Pi is that the Pi uses 3.3V TTL serial communication and the TT4 uses standard RS-232 (which is +/-5V minumum).?? With the kit version, either or both ports (A & B) can be set to TTL serial, and with the preBuilt PortB can be set to TTL serial.? BUT ...?? the TT4 is 5V logic, while the Pi is 3.3V logic.

Options:
1. Obvously you can use a Micro-USB to RS232 adaptor, but the really isn't a direct connection
??? No change in jumpers required.
2. Set TT4 JP7 for TTL on connected port and use the Pi pins 8 & 10 (3.3V logic serial) to pins 2 & 3? of J2 with resistors of the TT4.
??? Proper method would be 2 resistor voltage divider to drop the 5V to ~3.3V to the Pi RX pin (10).? Works at 19,200 baud.
??????? Resistors of TT4 2200 ohms to Pi and from there 4300 ohms to ground works well.
??? Some users will use a single resistor in the Pi RX pin (10)? to limit current.? I know lots of people that do this.
??? The 3.3V will be enough to toggle the TX pin of the TT4 so nothing needed there.
3. Use another MAX232 (not the correct part as this is 5V to RS232) chip to level shift the Pi to the TT4
??? No change in jumpers required.
4. Us a 3.3V to 5V level shifter (some are made for I2C).?
??? I have not tried this, but if it works for I2C, it should work for TTL serial.
??? Set TT4 JP7 for TTL on connected port.?

So your direct answer is, not without a few added parts/

Robert Giuliano
KB8RCO



On Friday, April 2, 2021, 4:07:02 PM EDT, Peter VE7PPE <ve7ppe@...> wrote:


My preferred setup is to combine the TT4 with a Raspberry Pi Zero W.? I have been using the TT4BT to provide serial to the Pi, but is there a place on the board I can easily? connect J2 pins 2&3 serial direct??

This would? cut the power consumed by 50ma and be a more reliable connection.

Thanks

 

I think his idea of saving current consumption stems from eliminating the existing MAX232 chip. All these things, i.e., splicing directly into the TTL UART lines of the TT4, bypassing the converter, etc. would probably be a lot easier to do with the older version/kit, where you can actually just pop the MAX232 out of the socket and stop it's current consumption and noise, and tap the TTL line directly. We use a 2 k and 1 K voltage divider to limit the 5 Volt TTL output to 3 Volts when it has to communicate with critters of that species, but any values of similar ratio will work. As Bob suggests, the TT4 will be fine with 3.3 Volt TTL inputs, its just the output that might be an issue. Doing these types of mod's to the surface mount TT4 could certainly be done, but it would be a bear to repair if you ever wanted to convert it back!?

Allen AF6OF


-----Original Message-----
From: Rob Giuliano via groups.io <kb8rco@...>
To: [email protected] <[email protected]>
Sent: Fri, Apr 2, 2021 6:11 pm
Subject: Re: [TinyTrak] connecting serial directly from TT4 board?

The issue with connecting directly to the Pi is that the Pi uses 3.3V TTL serial communication and the TT4 uses standard RS-232 (which is +/-5V minumum).?? With the kit version, either or both ports (A & B) can be set to TTL serial, and with the preBuilt PortB can be set to TTL serial.? BUT ...?? the TT4 is 5V logic, while the Pi is 3.3V logic.

Options:
1. Obvously you can use a Micro-USB to RS232 adaptor, but the really isn't a direct connection
??? No change in jumpers required.
2. Set TT4 JP7 for TTL on connected port and use the Pi pins 8 & 10 (3.3V logic serial) to pins 2 & 3? of J2 with resistors of the TT4.
??? Proper method would be 2 resistor voltage divider to drop the 5V to ~3.3V to the Pi RX pin (10).? Works at 19,200 baud.
??????? Resistors of TT4 2200 ohms to Pi and from there 4300 ohms to ground works well.
??? Some users will use a single resistor in the Pi RX pin (10)? to limit current.? I know lots of people that do this.
??? The 3.3V will be enough to toggle the TX pin of the TT4 so nothing needed there.
3. Use another MAX232 (not the correct part as this is 5V to RS232) chip to level shift the Pi to the TT4
??? No change in jumpers required.
4. Us a 3.3V to 5V level shifter (some are made for I2C).?
??? I have not tried this, but if it works for I2C, it should work for TTL serial.
??? Set TT4 JP7 for TTL on connected port.?

So your direct answer is, not without a few added parts/

Robert Giuliano
KB8RCO


On Friday, April 2, 2021, 4:07:02 PM EDT, Peter VE7PPE <ve7ppe@...> wrote:


My preferred setup is to combine the TT4 with a Raspberry Pi Zero W.? I have been using the TT4BT to provide serial to the Pi, but is there a place on the board I can easily? connect J2 pins 2&3 serial direct??

This would? cut the power consumed by 50ma and be a more reliable connection.

Thanks

 

I forgot about the 3.3v <--> 5.0v.? Sounds like I'm make things more complicated rather than simplifying.
Will work within the confines of BT, serial profiles here I come

Thanks for the input

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