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Heart rate monitor based on NXP MCU

Published time : 2018-01-18 NXP
The design is based on the intelligent design of the latest monitors from NXP MCUs, which are widely used in the medical field and provide better care for patients.

Solution Introduction

The latest monitors with NXP MCUs are intelligently designed to measure heart rate during exercise or strenuous exercise.

The new heart rate monitor consists of two main components: a signal acquisition sensor/transmitter and a receiver (watch or smartphone).

Today, signal acquisition sensors can even be integrated into the clothing worn by the user or patient. The NXP MCU analyzes the ECG signal and determines the heart rate.

This 8-bit MCU supports simple heart rate monitors; high-end 32-bit MCUs support more complex functions such as heart rate variability, activity levels, respiratory rate

Heart rate monitor based on NXP MCU block diagram

Heart rate monitor based on NXP MCU block diagram

Related electronic parts description from NXP

The MC34671 is a cost-effective fully-integrated battery charger for Li-Ion or Li-Polymer batteries. 

The high input voltage, up to 28V,eliminates the input over-voltage-protection circuit required in handheld devices such as cell phones, Bluetooth accessories and MP3 players.
A typical charge cycle includes trickle, constant-current (CC) and constant-voltage (CV) charge modes. The CC-mode current is
programmable up to 600mA with an external resistor. 

The voltage across the external resistor is also used to monitor the actual charge current. 

The constant voltage is fixed at 4.2V with 0.7% accuracy over a -20°C to 70°C temperature range. 

The trickle-mode current is preset to 20% of the CC-mode current when the battery voltage is lower than the trickle-mode threshold. 

The end-of-charge (EOC) current threshold is preset to 10% of the CC-mode current to save the board space and cost. 

A charge current thermal foldback feature limits the charge current when the IC internal temperature rises to a preset threshold.
The MC34671 also protects the system with its input over-voltage protection (OVP) feature. In addition, the MC34671 has a 2.6V falling power-on-reset (POR) threshold, making it perfect to work with current
limited power supplies. 

Three indication pins (PPR, CHG and FAST) can be simply interfaced to a microprocessor or LEDs. 

When no power supply is connected, or when disabled, the charger draws less than 1.0µA leakage current from the battery.
Features
• No external MOSFET, reverse-blocking diode or current-sense resistor are required
• Guaranteed maximum 600mA programmable CC-mode current
• ±0.7% voltage accuracy over -20°C to 70°C
• ±5% current accuracy over -40°C to 85°C
• 28V maximum voltage for the power input with 11V over-voltage protection threshold
• 2.6V minimum input operating voltage
• Trickle charge for fully discharged batteries
• Charge current monitor
• Charge current thermal foldback
• Pb-free packaging designated by suffix code EP

Key Components

No. Part Number Manufacturer
1 MK50DX256CLK7 NXP
2 MK53DX256CLQ10 NXP
3 MC34671AEPR2 NXP