Trouble with programming baud rate for HC-05 Bluetooth module

Projects Networking, Protocols, and Devices
1

I've been trying to add an HC-05 Bluetooth module to my Uno, in order to be able to program the Uno with Bluetooth. When I try to run the serial sketch to reprogram the baud rate of the Bluetooth module from Steps #3 & #4, I get strange serial readings. Instead of receiving an "OK" I receive a series of strange characters at random intervals.

I've been following the instructions from Make here:

DIY Arduino Bluetooth Programming Shield

The sketch used to calibrate the Bluetooth module to allow it to upload a program is:

/* Serial Loop */

#include <SoftwareSerial.h>

#define rxPin 8
#define txPin 9

SoftwareSerial mySerial(rxPin, txPin); // RX, TX
char myChar ;

void setup() {
Serial.begin(9600);
Serial.println("AT");

mySerial.begin(38400);
mySerial.println("AT");
}

void loop() {
while (mySerial.available()) {
myChar = mySerial.read();
Serial.print(myChar);
}

while (Serial.available()) {
myChar = Serial.read();
Serial.print(myChar); //echo
mySerial.print(myChar);
}
}

After uploading the sketch, you input these serial commands to reprogram the HC05's baud rate and assign the Rx and Tx pins:

AT+ORGL

AT+ROLE=0

AT+POLAR=1,0

AT+UART=115200,0,0

AT+INIT

I've tried searching for an answer but have not made much progress. Any help would be appreciated.

2

I was finally able to upload the coding. It turns out that jumping the Key and State (or EN and STATE on my board) did not switch my HC-05 into AT mode. Instead, I had to hold the reset button on the HC-05 before supplying power to it, without Key and State jumpered.

When Key and State pins were jumpered, the LED on the HC-05 did not come on, giving me the impression that a fail safe had been activated on the board somewhere. It seems that there is some variability in how to get into AT mode on the HC-05.

3

Now I've moved onto the next issue: when trying to upload a program over bluetooth, the HC-05 does not seem to be resetting the Uno, which is needed for the bootloader.

I wired a jumper to pin 32, which is connected to a 10nf capacitor. The capacitor is connected to a terminal that includes a path to the reset switch, 10k resistor to ground, and a 15k resistor to 5v.

Do all these connections need to be in a specific order, or should connecting them together work? Is my problem somewhere else in the circuit?

Any assistance with this project would be appreciated. Thank you for bearing with me.

4

yoyomankind:
I wired a jumper to pin 32, which is connected to a 10nf capacitor. The capacitor is connected to a terminal that includes a path to the reset switch, 10k resistor to ground, and a 15k resistor to 5v.

Do all these connections need to be in a specific order, or should connecting them together work? Is my problem somewhere else in the circuit?

You seem to have this all a bit wrong. First the capacitor should be 100nF (0.1uF) and not 10nF.
You say "the capacitor is connected to a terminal that includes a path to the reset switch" but is this a direct route or via other components that may effect the signal.
The 10K resistor should go to 5V and the 15K resistor to GND not how you described.

To prove the problem is the reset circuit and not other wiring you could try holding the reset button on the UNO down and click upload in the IDE (with a simple sketch like blink). Just as the Compiling Sketch... changes to Uploading... release the reset button. You may need to try this a few times to get it working but if it does work then it's just the reset circuit is at fault. Maybe 10nF is to small to trigger reset.