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A 3-Channel UHF Rolling-Code Remote Control, Pt.1

This high-security 3-button UHF transmitter and receiver can be used for keyless entry into homes and commercial premises and for controlling garage doors and external lighting. Three separate outputs on the receiver can be used to activate various electrical devices such as a door strike, a motorised garage door and 230VAC lights. Up to 16 transmitters can be used with the one receiver so it's even suitable for a small business.

By John Clarke

Features

Transmitter
• Three function buttons
• Coding randomisation
• Rolling code UHF transmission
• Registering ability
• 16 identifications encoding
• 12V remote control battery operation
• Keyfob case
• Acknowledge LED indication

Receiver

• 12V DC plugpack operation
• For use with up to 16 separate transmitters
• 3 independent 230VAC rated relay contact outputs
• Door strike driver output
• Momentary or toggle operations for each output
• Momentary outputs adjustable in duration from
0.26 seconds to 4.4 minutes
• Acknowledge, power and output LED indicators
• Look-ahead feature for 100 codes when transmitter code is ahead of receiver code
• Lockout available for any registered transmitter
• Local control of outputs available

Specifications

Transmitter

Battery: ..............................12V 55mAH (A23 type)

Battery life: ........................ >2.5 years expected with typical use

Standby current: ............... Typically 2.5μA with switches open (drawing 22mAH/ year from battery)

Code Transmit current: ...... 3mA average over 160ms (133nAH / transmission drawn from battery)

Register Transmit current:.. 3mA average over 2.75s

Randomisation current: ..... 3.3mA

“Stuck switch” current: ...... 220μA (after transmission is ended if a switch is kept pressed)

Code transmission rate:...... 1.024ms/ bit (1k baud)

Encoding: ........................... A high (or a 1 bit) is transmitted as a 512μs burst of 433MHz signal followed by 512μs of no transmission. A low (or 0 bit) is transmitted by a 512μs period of no transmission followed by a 512μs burst of 433MHz signal.

Rolling code: ..................... Sends four start bits, an 8-bit identifier, the 48-bit code plus four stop bits. The start bits include a 16.4ms gap between the second start bit and the third start bit. Code scramble value is altered on each transmission.

Register code:.................... Sent as two blocks. Block 1 sends four start bits, the 8-bit identifier, a 32-bit seed code and four stop bits. Block 2 sends four start bits, a 24-bit multiplier, the 8-bit increment and 8-bit scramble values, and four stop bits. The start bits include a 16.4ms gap between the second start bit and the third start bit.

Code randomisation: ......... Alters the multiplier values, the increment value, the scramble value and the seed code at a 40μs rate.

Transmission range: .......... 40m minimum


Receiver

Power: .............................. 12VDC at 150mA. (If using an electric door strike up to 12VDC at 1A intermittent)

Standby current: ................14mA (168mW) with all relays off. 150mA (1.8W) with all 3-relays and indicator LEDs lit

Relay contact rating: ..........10A @ 240VAC

Momentary period: ............ When set to momentary operation, each output is adjustable from 0.26s to 2s

in 0.26s steps, then in 1s steps to 10s and in 15s steps to 4.4 minutes. See Table 2.

Maybe you have been thinking of building the low-cost UHF remote switch which was featured in the January 2009 issue of SILICON CHIP.

That was mainly intended as a cheap replacement for garage door controls and any application where security is not paramount – for example, when the garage does not have internal access to the home. This completely new design is for applications where you want high security and the ability to control more than one device.

For example, you may want to control a garage door (one or two) and your house lights to illuminate the driveway or entry. Or maybe you want to control the garage door, the driveway lights and have keyless entry into your home.

After all, you already have keyless entry into your car; why should you have to fumble with keys to open your front door? In fact, there are already commercial keyless entry systems for homes. Why shouldn’t you have it too. . . and at lower cost?

Or how about this scenario? Say you have a 2-car garage in which the cars are tightly parked with not enough room for the passenger to get in before you drive out.

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