Center 301 3.5mm to RS232 Cable

Discuss roast levels and profiles for espresso, equipment for roasting coffee.

#1: Post by ballpencil »

Calling out owners of this cable.

Center 300 series thermometers have 3.5mm jack for their RS232 interface output. Some models come stock with the cable and some you need to buy the cable separately.

I figured i can make this cable myself but i need to know the pinout. It's just three pins from the 3.5mm audio jack but i need to know where they go to the DB9 connector. Perhaps anyone can help me with this? This is one sample. As you can see, only pin 2,3 and 5 are used on the DB9 connector. I'm almost certain pin 5 goes to the base. I'm just not sure about pins 2 and 3. It's a long shot, but can anyone with this cable and a tester help me?

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#2: Post by civ »

ballpencil wrote: Center 300 series thermometers have 3.5mm jack for their RS232 interface output.
This is a very common/basic interface with just TXD (transmit) RXD (receive) and GND (ground) cabled to the corresponding pins on a DB9 serial connector. Somewhere I have a Tenmars TM-712D Datalogger that uses this same type of RS232 cable (can't find it)

The pinout of the RS232 side is like this:

Image: courtesy of USConverters

The ones that matter to you are pins 2 (RXD), 3 (TXD) and 5 (GND).

Your drawing seems correct, with the black wire going to pin 5 (GND) and the other two cables going to pins 2 (RXD) and 3 (TXD).
If I recall correctly (been there, done it a few times), if you wire it pins 2 and 3 the wrong way around, it just won't work as it will be transmitting/receiving in the wrong direction.

ie: TXD Center 300 -> TXD PC and RXD Center 300 -> RXD PC instead of TXD -> RXD and RXD -> TXD PC.

Just be careful to use the right pins. ie: 2 (RXD), 3 (TXD) and 5 (GND).

Maybe someone with more experience can chip in.

Let us know how you fared with this.



ballpencil (original poster)

#3: Post by ballpencil (original poster) »

Exactly, even if i swapped pins 2 and 3, it will only not work and should not damage anything. It will only take me 10-15 more minutes to desolder and swap the pins but hey if i can get it right the first time, why not. I plan on using a cheap serial to bluetooth module so i can go wireless. I will report back any result. Thanks

Team HB

#4: Post by ira »

If it's real RS232 then you essentially can't hurt it no matter how you swap the wires or what you connect it to, but if it's fake TTL level RS232 it can be damaged by hooking it to something else. Checking for ground should be easy as it probably connects directly to battery ground negative.


ballpencil (original poster)

#5: Post by ballpencil (original poster) »

Small update. Just made the purchase on the Center 301 and a PL2303 based serial to USB cable and waiting for them to be delivered. Had good experience with Profilic chipset before (serial to usb conversion can be finicky sometimes) so i chose PL2303. There are four wires from the converter:
++ Red: +5V
++ Green: Tx
++ White : Rx
++ Black: GND
but obviously i'll be using only the Tx, Rx and GND. Can anyone confirm: TXD from the Multimeter gets connected to Rx (white wire) on the PL2303, right?

Just need a visit to an electronic shop nearby to get the 3.5mm jack.

ballpencil (original poster)

#6: Post by ballpencil (original poster) »

Final Update, it works!

Surprisingly, the provided manual book was very helpful. Not something i would expect from Chinese electronics.
There's a diagram to the 3.5mm pin designations.
All i did was connect TX - RX from the meter to RX - TX on the PL2303 serial to usb converter, respectively. Of course, ground as well.
Had some trouble with driver installation but it was resolved after full removal and installation of it.


#7: Post by Hadean »

Hi Ballpencil

Could you give me a picture of the other page in the manual?
My Center 301 didn't come with a manual and I need to know those commands listed on the 2nd page!



#8: Post by Hadean »

If you could also share a link to the USB/RS232 cable you purchased, it would be appreciated!

ballpencil (original poster)

#9: Post by ballpencil (original poster) »

Here you go..

Page 10 is the last page.
As for the USB/RS232, just search for PL2303 USB RS232 converter on any of your favority online market.


#10: Post by Hadean »

Thanks so much!