How to build a voltage level shifter that shift 3.3V to 6.6V and vice versa

Question

I need to communicate a microcontroller (Btm, Arduino Uno) that it reads 3.3 V as (1) and 0 V as (0), with another microcontroller (Top, Arduino Uno) that reads voltage 3.3 V as (0) and 6.6V as (1) and it is the same for its output voltage. In order for them to communicate with each other, I need to increase microcontroller (Btm) logic (1) voltage from 3.3 V to 6.6 V, vice versa from 6.6 V to 3.3 V for microcontroller (Top) logic (1). For their low voltage I could use voltage divider from Top to Btm and there should be no problem for low logic to communication from Btm to Top.

The Power Supply is DC supply, and currently I am focusing on the correct communication of High and Low logic between both microcontrollers. I am attempting voltage stacking with microcontrollers to see the effects of it but the data communication issue was observed as a effect.

My question is what kind of circuit should I build so that I can achieve this?

---

I had stacked MCUs together. The arrangement looks something similar to diagram below, I had trouble for them to communicate with each other. As the microcontroller (Top) output will be read as high regardless logic 0 or 1, and microcontroller (Btm) output will be read as low regardless logic 0 or 1.

Answer 1

Voltage Source Offset

The following two circuits add a 3V "floating battery" (1mA flowing through R2, R4) between the top and bottom nodes.

The circuit on the left passes signals from top MCU to bottom MCU. The circuit on the right passes signals from bottom MCU to top MCU.

^{simulate this circuit – Schematic created using CircuitLab}

It's also possible to have a bidirectional circuit:

^{simulate this circuit}

You'll need one such circuit per signal. Do not share the reference transistor outputs unless they are buffered by an opamp. For example:

^{simulate this circuit}

The reference levels have to be buffered:

^{simulate this circuit}

Current Switcher

This one is quite a bit faster since nothing saturates. Q1 and Q2 direct the current from Q5 through one of the two branches, based on the logic state at A. Either Q1 or Q3 is active, and they steer B to follow A. Q7 and Q8 provide voltage clamping on B, establishing a valid output range and preventing saturation of Q3.

^{simulate this circuit}

That circuit has input on the top, output on the bottom. For the other direction, mirror the schematic along the horizontal axis, and swap transistor polarity (PNPs with NPNs).

Answer 2

This simple solution isn’t sufficient? Even with “slow” BC847 & 857 it can be used up to 500kHz.

500kHz input signal:
(Blue is input, green is output)

Edit:

There is an option to use a two NPN inverter. The output pulse will be more symmetric and the overall delay will be splitted to both edges, so half of delay will contain rising edge and half falling:

Answer 3

Bottom MCU output is voltage source V3. Top MCU inputs are nodes in1...in3. Diodes shown are the MCU's input protection diodes, could also be added as BAT54S for example.

On the left: capacitive coupling. Cheap and fast, but does not pass DC. Input protection diodes take care of holding the voltage more or less in the right window.

Middle: using a transistor as common base stage to do the voltage translation. Cheap and slow, passes DC. Simulated with the ubiquitous MMBT3904. Power consumption is proportional to speed, because higher value resistors will give slower rise/fall times. I adjusted resistor values to avoid saturation in the BJT. The top resistor has a little higher value to compensate for Vbe drop on the bottom resistor. It would also work with a low threshold MOSFET, for example XP221/XP222, but Vgs has more spread, which would make output levels less accurate.

Right: combining the two gives a cheap, fast, low power circuit that also passes DC.

To operate in the other direction, simply flip and use a PNP.