Screenblock™
rations your children's screen time.

Technical information
 

Dimensions

Click here to see Screenblock dimensions.

How do the tokens talk to Screenblock?

The tokens (fobs and cards) communicate with Screenblock through what can only be described as a miracle of technology.  There is a short range coil around the display which transmits a carrier frequency of 125Khz.  If a token is bought into the range of the coil (about 50mm), the token which also has a small coil, picks up the 125Khz and turns it into enough electricity to power up a silicon chip.  Using this power and the two coils the token chip will carry out an encrypted conversation with Screenblock. The conversation lasts about a quarter of a second.  When the token is moved out of range of Screenblock's coil, it will power down.  There are no moving parts or batteries involved and the lifetime of this system is virtually unlimited.

How is the current measured?

The flow of current is measured by a sensing device made by General Distribution Ltd.  It is an encapsulated wound circular ferrite with the power wire going through the centre.  This signal is picked up and amplified by an op-amp.

How is the LED brightness set?

We are using an exciting new EPROM resistor package which we can write a value to. The package remembers this value and adjusts its resistance and hence the brightness of the LEDs accordingly.

What provisions are there for backup power?

On the main circuit board, there is a replaceable Lithium battery.  This battery will power the Real Time Clock for up to 10 years.  If Screenblock is connected to the mains (house current), then the battery power is not used but held in reserve.  Also on the circuit board is non-volatile memory which keeps all the settings indefinitely if there is a power failure.

How do I reset Screenblock?

Unlock Screenblock with the keys and remove the lid. Press and hold down the ‘On’ and ‘Override’ buttons for 5 seconds. The unit will give 4 bleeps to confirm the reset. Turn Screenblock off and then on. In this state, all settings are lost except the time. Screenblock will have to be setup again by enrolling the tokens and setting the time allowance.  (see instructions).

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