Hi everyone,
I am working on a bluetooth programming shield for my Arduino Uno based on a HC05 module. In tutorials by other people I often see they use resistors because apparently, the RX and TX on a HC05 are 3.3v rated and an Arduino Uno is 5v rated. However, my module says level: 3.2v - 6v. (image included). Do I still need to bother with the resistors?
Adding a 1K resistor between the Arduino TX and the Bluetooth RX is all you need. It doesn't hurt, and cost you nothing really.
// Per.
Zapro:
Adding a 1K resistor between the Arduino TX and the Bluetooth RX is all you need. It doesn't hurt, and cost you nothing really.// Per.
Thanks for the reply! Yeah I understand I doesn't hurt, but the question is more like in a broader sense: Am I correct that level: 3.2v-6v indicates that the TX/RX signals will work on those levels? Or is this indicating something else? (I thought like maybe it indicates what will pass for a 'High' signal for the key)
I think, strictly speaking, HC05 is the module that is typically sold for hobby use on a carrier board that has some additional circuitry. The one I have in front of me is labeled "ZS-040".
The silkscreen for this board is "Power: 3.6V-6V" suggesting it has a low dropout regulator from that voltage down to the 3.3V used by the HC05 module. It also has the label "Level: 3.3V" adjacent to the RXD and TXD pins, suggesting that is the voltage limit for those pins. There may exist adapter boards that include level conversion for the serial pins, but unless one knows that to be the case, it should be incorporated in the system design.
Adding a 1K resistor between the Arduino TX and the Bluetooth RX is all you need.
No you need a potential divider between the Arduino TX and Bluetooth RX. I use a 510R and 1K.
The single resistor will not cut down the voltage it will just limit the current as the anti static diodes conduct with the voltage being too high. While a single resistor might function it is stressing the Bluetooth device and this will therefore have a higher MTBF rate ( Mean Time Between Failures ) that it otherwise would.
Grumpy_Mike:
The single resistor will not cut down the voltage it will just limit the current as the anti static diodes conduct with the voltage being too high. While a single resistor might function it is stressing the Bluetooth device and this will therefore have a higher MTBF rate ( Mean Time Between Failures ) that it otherwise would.
In general it's absolutely not a problem letting the substrate diode absorb the 1.7mA.
// Per.
In general it's absolutely not a problem letting the substrate diode absorb the 1.7mA.
The only problem is the reduced MTBF that results. If you want to live with that then fine, but it is extremely bad engineering practice and all for what? Saving a resistor, big deal.
