SparkFun Forums

[TobyA]

Hi there,

I am referring to the https://www.sparkfun.com/products/11978 for the following.

I have a standalone ATMEGA328 chip that connects with a 3.3V serial device. The ATMEGA328 is powered by a 3.7V lipo battery (voltage varies between 3.5 - 4.2V). I am running the ATMEGA328 at 8MHz.

Considering that the voltage for the ATMEGA328 is varying with the lipo battery when sending serial to the device, can this board still convert 3.5 to 4.2V down to the required 3.3V for the serial device?

Thanks for your time

[skimask]

Might be nice to know what this "serial device" is...

[TobyA]

Sorry, it is a HC-05 bluetooth module.

[Mee_n_Mac]

Considering that the voltage for the ATMEGA328 is varying with the lipo battery when sending serial to the device, can this board still convert 3.5 to 4.2V down to the required 3.3V for the serial device?

Yes and maybe. The "rx" circuits are just voltage dividers, 10k over 20k. So the rx_lv out is 0.6666x of the rx_hi voltage input. Thus 3.5v in (from the Arduino tx output) yeilds only 2.33v out to the BT rx input. Will that be sufficient to register a logic 1 at the BT module ? Perhaps, but if it works there will be little noise immunity.

The tx circuits are a FET, that shorts the hv output to ground when the tx_lv input is a logic 0. When the input is a logic 1, the FET is off and the output is pulled up to whatever the hv voltage is. So that should still work.