HC05 not getting data from PC terminal

Thread Starter

spinnaker

Joined Oct 29, 2009
7,837
I have 3 of those HC-05 Bluetooth devices. An old one and a two new ones. The old one was having issues so I decided to order a couple of new ones.

In addition to some flaky connection issues, the old one was not receiving data from the terminal. Mo data on the Txd pin as measured by my scope.

The old one started working for some unknown reason. I put the project aside for a bit and got the two new HC-05s in.

One of the HC-05s worked perfectly and continues to work. But the other is experiencing the same issue as my old HC-05. No data on the Txd pin when data is being transmitted from the terminal software. So I hooked up the old one. The old issue is back. No data on Txd.

What I noticed about the working on is TxD is always high until data is transmitted then the pin goes low.

The two that are not working, the TxD pin is always low.

I find it a bit odd that I have two HC05s purchased at different times. Makes me think I might be doing something wrong but then again one works.

I have En tied high. Also tried letting it float. Vcc is at 5V. Nothing other than my scope probe is on Txd pin.
 

turboscrew

Joined Dec 7, 2018
16
Does it have the status LED? Or mode change button?
Or what's the level on KEY-pin? Or is that the En-pin?
From a manual:
"If it is input low level or connect to the air, the module is at paired or communication mode.
If it’s input high level, the module will enter to AT mode."
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,837
LED, button and EN pin.

It is not in AT mode. Light is not slw blink and it will send data from the Pic to the terminal.
 

turboscrew

Joined Dec 7, 2018
16
Hmm, came to think about the output... I think it's common that serial line is high when it's idle. When the sending starts, it goes low (for start bit).
As if the non-working devices started to send, but froze...

I found two different HC05s in the net, but neither of them had En-pin. One had a button and a LED, the other one didn't.
Do you have a link to the ones you have?

Do the LED blink at all? I found one document that named one pin "enable/key". In that document it says about the LED:
"Indicates the status of Module

  • Blink once in 2 sec: Module has entered Command Mode
  • Repeated Blinking: Waiting for connection in Data Mode
  • Blink twice in 1 sec: Connection successful in Data Mode"
 
Last edited:

turboscrew

Joined Dec 7, 2018
16
Oops, the pinmap and the text under the connection diagram disagree...
Maybe it's good to try both ways.
But the pin should be tied to ground (for the button to work).
 
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