V to Hz 3 Click is a compact add-on board that converts an analog voltage input signal into a specific frequency pulse wave signal. This board features the AD7740, an ultrasmall synchronous voltage-to-frequency converter from Analog Devices. The AD7740 has a linear response, so applying a voltage from 3V up to 5V on its VIN terminal will generate the pulse with a frequency linearly proportional to the input voltage. It contains an integrated 2.5V bandgap reference defining the span of the VFC and can be overdriven using an external reference. The full-scale output frequency is synchronous with the input clock signal provided by the LTC6903 programmable oscillator, with a maximum input frequency of 1MHz. Based on the analog input value, the output frequency goes from 10% to 90% of the input frequency. This Click board™ is the most suitable for low-cost analog-to-digital conversion, linear frequency modulation, voltage-to-frequency conversion, and as a variable clock signal generator.

V to Hz 3 Click as its foundation uses the AD7740, a CMOS synchronous Voltage-to-Frequency Converter (VFC), which uses a charge-balanced conversion technique from Analog Devices. The input voltage signal from 0V up to 5V from its VIN terminal is applied to a proprietary front-end based around an analog modulator that converts the input voltage into an output pulse train. Depending on the analog input value, the output frequency goes from 10% to 90% of the input frequency provided by the SPI-configurable LTC6903 programmable oscillator, with a maximum input frequency of 1MHz.

The analog input signal to the AD7740 is continuously sampled by a switched capacitor modulator whose sampling rate is set by a main clock (primary input frequency of the AD7740). The input signal may also be buffered, setting the BUF pin of the mikroBUS™ socket to a high logic state before being applied to the sampling capacitor of the modulator, isolating the sampling capacitor charging currents from the analog input pin. The AD7740 also contains an on-chip 2.5 V default bandgap reference, the reference input to the core of the AD7740 defining the span of the VFC. Alternatively, an external reference may be used to overdrive the internal reference by applying it to an onboard header marked as REFIN.

Alongside SPI communication, this Click board™ also uses several additional pins. The BUF pin mentioned above represents the Buffered mode selection, while the AN pin indicates the presence of an external analog signal. The last of the enabled pins is the F signal, routed to the INT pin of the mikroBUS™ socket, which can also serve as output frequency from the AD7740 in the same way as the FOUT terminal.

This Click board™ can operate with both 3.3V and 5V logic voltage levels selected via the VCC SEL jumper. This way, it is allowed for both 3.3V and 5V capable MCUs to use the communication lines properly. However, the Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used, as a reference, for further development.

• Interface: SPI
• Compatibility: mikroBUS™
• Dimensions: 42.9 x 25.4mm
• Input Voltage: 3.3V or 5V, External
• Supply Voltage: Min. 3.3V, Max. 5V
• Analog Input Range VIN: Min. 0V, Max. 5V
• Output Frequency Range FOUT: 1 MHz
• Operating Temperature Range: Min. -40°C, Typ. +25°C, Max. +105°C

• Schematic
• AD7740 Datasheet
• LTC6903 Datasheet
• mikroSDK
• LibStock