Figure 1-1 Simplified Block Diagram for Video Doorbells

See the interactive online End Equipment Reference Diagram for a more complete view.

It is often desirable to have the system controller for a battery powered device such as a video doorbell to be as low voltage as possible. Reducing supply voltage reduces power consumption significantly; this reduction in voltage, however, also limits the peripherals that can be operated. It is very common for wireless interface modules to need at least 1.8 V supply and signal levels, sometimes requiring as much as 5 V for the supply.

Figure 2-1 SPI Translation for System Controller to Wi-Fi™ Module Interface

Serial Peripheral Interface (SPI) provides up to 10 Mbps of data transfer and is typically used for this type of communication. There are two common solutions used for translating the voltage of this interface using either the TXB0104 or the SN74AXC4T774 voltage translators.

TXB0104

• Auto-bidirectional: No direction configuration required
• Works for 1.2 V to 5 V translation
• 20 Mbps per channel at 1.2 V operation

SN74AXC4T774

• 100 Mbps at 1.2 V operation
• Requires direction configuration; typically hard-configured to unidirectional translation
• 3.6 V maximum operating voltage