I was able to set up a remote serial link successfully after several days of learning/experimenting. I am documenting my solution so that others can benefit. It was frustrating but eventually worked very well. I purchased two of these DSD HC-05 units to set a remote serial link between my robot car and my laptop. These units cannot connect to iPhone per seller description and I can confirm it. I could not get my windows 11 laptop to reliably connect to these either. Using "advanced discovery" I could see the devices but pairing fails almost immediately. Not sure if this is an issue with my laptop or with the devices. I had to buy a 2nd unit in order to have the two talk to each other. One HC-05 is now connected to my laptop through Arduino Uno and the other will be connected to my Robot car. Here is the process I finally came up with. If your laptop connects to the HC-05 then I suppose you could manage with one Uno/HC05 pair. Need to set up one HC-05 to act as master and set a few AT parameters. The second HC-05 operates as slave (default HC-05 mode) but we need to get it's address. Have to get the devices into AT mode to get these steps done. To enter AT mode: Connections between HC-05 and Uno R3: HC-05 Pins (left) -> Uno R3 Pins (Right) GND->GND, VCC->5V, EN->3.3V, Rx->Rx, Tx->Tx. HC-05 State Pin left Open HC-05 gets power from Uno R3 and Uno R3 gets power from Laptop USB CAUTION: You should use a resistor divider any time a signal goes in to HC-05 Rx. Don't need one for Tx. Search the web. I used 1K and 2K resistors. I omit that here for simplicity in explaining but I am using one and highly recommend you use it. Connect USB from Uno to Laptop, fire up Arduino IDE on laptop, set IDE baud rate to 38400 with both "NL & CR" option selected. Select board and COM Port on IDE. Load the "null sketch" on to the Uno R3 from Arduino IDE. Null sketch: Setup and loop declarations with no code - Arduino IDE "new sketch". Do NOT add any code. Type AT hit enter then repeat in the IDE monitor input window [responses show up in the output part of the window below the input line] First AT will give you an Error response, ignore, do it again and you should see OK - means you are in AT mode. If HC-05 is in AT mode you will see the Red onboard LED slow flashing. I used the following commands to get address of the Slave before I did anything with the Master Slave HC-05 AT commands: AT+ROLE? should see +ROLE:0 which is Slave AT+ADDR? should see +ADDR:xx:xx:xxxxx [note this down, in some cases there many be fewer digits fill in 0's in front for that section]Label this HC-05 as Slave [i just used some tape to write on] Disconnect USB from Uno, disconnect Slave HC-05 from Uno Connect Master HC-05 to Uno exactly as above then follow all same steps except use the following AT commands: Master HC-05 AT commands: AT+ROLE? should see +ROLE:0 AT+ROLE=1 should see +ROLE:1 OK which is now set as master AT+CMODE=1 should see +CMOD:1 OK which now limits HC-05 Master to connect to only 1 specified address AT+BIND=xx,xx,xxxxx should see +BIND:xx,xx,xxxxx OK [Need exactly number of digits as shown, replace ":" from above with "," fill in any missing digits as preceeding 0's Label the HC-05 as Master Now we need to set up the HC-05 and Uno R3's for normal operation (no longer AT mode). Remove the EN->3.3V and leave it open Connect the two HC-05 to their respective Uno R3's, leave EN open, remove HC-05 Rx, Tx for now. Same for both Master and Slave. If you power up the two Uno R3's along with the HC-05's you should see the onboard red LED flashing in unison - this means the two have paired up. Write sketches for master and slave [I am including my sample sketches below] Leave the HC-05 Rx and Tx disconnected while you upload the sketches for master and slave. The sketches will NOT load if Uno Rx and Tx pins used for anything else. AFTER sketches are uploaded - connect both Master and Slave Rx and Tx to their respective Uno R3's. But this time they are SWAPPED on both Master and Slave. Rx->Tx and Tx->Rx. Recall the CAUTION re using the voltage divider. Rest is same as before except EN is open. This worked for me ... hope it helps you. The weblinks provided in the included documentation are hard to reach. Some of the specific links provided worked but others did not. I docked a star for that. Without that I would give them 5 stars. Hard to start up but once it works it's great! The devices are well made, especially, like the protective plastic covers. Sketches used in the review: [note: during operational mode to connect to laptop to master Uno/HC-05 while it's acting as master, I had to use Software Serial in the master. Beyond scope of this review but not hard if have the basic code below working] // null sketch void setup() { } void loop() { } // end null sketch // Uno_HC05_Master_LED.ino // HC-05 Master turns on External LED & writes to HC-05 Slave to turn on remote LED // Note HC-05 Rx to Uno Tx via resistor divider, HC-05 Tx to Uno Rx di...
