Inside the Schick Hydro microcontroller-powered wet razor
Patrick Mannion -May 16, 2012
Microcontrollers are everywhere, including the oddest of places, such as a razor—the Schick Hydro Power Select customizable power razor, to be precise. I’m not sure why you’d need microcontroller-controlled customizable power or the packaging, waterproofing, and power issues that go along with it, but I gave it a shot. After all, Schick promises it “allows men to interact with their razor in a new way.” I never realized that I longed to interact with my razor in new ways, but Schick has created a demand—a craving, if you will—and I just had to try it. Alas! It wasn’t all that much better than interacting with my regular arm-powered, hand-controlled razor, so I instead took it apart. It’s a bit more interesting to go inside and see how the designers implemented a wet razor, powered from one AAA battery and featuring three vibration settings, easy-to-read indicators, and a haptic sensor. Why they would do it is another question.
1. A three-stage power button sets the vibration. The razor rotates through all three settings and then goes into off mode. It required too much pressure to activate due to its sealing cap.
2. A vibration-stage indicator uses LEDs.
3. Batteries are inserted here.
4. Removing the cap exposes the AAA battery. These batteries have a peak voltage of 1.8V but drift down to 0.9V over time.
5. The battery holder attaches firmly to the PCB using a solder joint and clips.
6. The internals, with plastic and rubber sealing removed, expose the unbalanced motor that vibrates the razor. Unlike a toothbrush motor with an actuator that rotates the heads, this motor doesn’t connect to the razor blades. It simply causes the razor to vibrate. If anyone has found this vibrating feature on a razor to be useful, please let me know. I may be missing something.
7. The razor has a three-stage power switch.
8. A Microchip MCP1624 low-voltage input regulator boosts the battery’s voltage to the 2V that the Microchip PIC10F222 microcontroller requires. The regulator maintains that 2V over the life of the battery, even as it drifts over time from 1.8 to 0.9V.
9. At the heart of the Hydro Power is the PIC10F222 microcontroller, again from Microchip. This six-pin, 8-bit device has 768 bytes of flash memory that sells for 40 to 79 cents (www.datasheets.com). It controls almost everything, including the motor, through an on-chip PWM controller.
Editor's Note: A friend of mine was kind enough to provide more details and pointed out some items I forgot to mention above, such as the motor being a precision metal-brush dc motor. But wait, there’s more, a lot more: Here is a board breakdown, followed by a functional description of the overall module:
The module can be split into the following parts:
- dc/dc converter (raise/conditioning of battery voltage)
- Peripherals (switch, LEDs, motor)
- Other components
-AAA-size battery was selected due to size, acceptable weight, sufficient capacity, availability worldwide
dc/dc converter (raise/conditioning of battery voltage):
-Raise of battery voltage 0.8 to 1.6V to stable 3.0V
-Allows use of battery’s capacity up to 80%
-3.0V required to run LEDs and microcontroller
-Stable/distortion-free power supply for the microcontroller
-Stable reference voltage supply to determine battery status
-Minimal continuous power consumption of approximately 70 μA (in sleep mode)
-The architecture of the 10F-microcontroller family from Microchip meets our requirements regarding size, cost, flexibility
-Reliability, and power consumption: The microcontroller hosts the prepreprogramed software and controls the components based on the user interaction and the battery status
-When the battery is inserted the microcontroller is always on:
- mode: software execution mode according to programmed commands
- mode: sleep mode, minimal power consumption, waiting for user switch action then going to 1. mode
-Motor speed adjustment and corresponding LEDs
-Device on/off, sleep mode
-Auto switch-off to sleep mode after 13 minutes run time (protects device from accidental turn-on)
-Power-up sequence: self-test when changing the battery (short pulse on all LEDs and motor)
Peripherals:-One micro push button for start/stop and select speed (this pulse switch type is not cutting off power supply)
-Three green speed LEDs show the selected speed of the motor (low, medium, high)
-Two battery LEDs indicate the battery status:
- green = battery ok
- red continuous = a few shaves left
- red flashing and no motor = change battery
- at battery exchange: battery reset to green at battery voltage > 1.35V
Other components (resistors, transistors, capacitors, diodes):
-Only a few other low-cost components are needed to:
- measure and indicate the battery voltage
- drive the motor
- drive the LEDs