BV4115. RF Packet Transmitter. Product specification. February ByVac 2007 ByVac Page 1 of 5

Transcription

1 Prduct Specificatin Prduct specificatin. February 2007 ByVac 2007 ByVac Page 1 f 5

2 Prduct Specificatin Cntents 1. Dcument Versins Intrductin Features Battery Life Blck Diagram External Cnnectin Pwer PO Vref Analgue Channels LED Packet Descriptin Addressing & Perids Setting the Address Dcument Versins 1.00 February Intrductin This is a lw data rate shrt range packet transmitter intended fr remte sensing applicatins. The packet transmissin rate can be varied frm 1 secnd t 2 minutes, this will effect the ttal pwer cnsumptin and thus battery life. Typical applicatins wuld include remte temperature r weather sensing, alarm triggers, dr mnitring etc. The device sends ut a fixed packet f infrmatin that can be received by the RF Packet Receiver r the RF Packet transceiver. There are tw analgue inputs t the device that will reflect the vltage applied t them. The cnversin is 10 bit and the rate will depend n the transmissin rate. 3. Features Eight addresses cnfigurable by push buttn, retains cnfiguratin when pwer remved. Very lw pwer cnsumptin, designed fr battery peratin. Eight packet rates variable frm 1 secnd t 2 minutes RF Transmitter, MHz, apprximately 100m range. Packet transmitted at 2400 Baud. Tw 10 bit analgue inputs, 1 reference vltage Small 25mm x 19mm PO cnnectin fr driving external cmpnents. 10 digit A t D giving a range frm 0 t Analgue ref input. 4. Battery Life The primary intensin fr this device is t cnstantly send infrmatin fr its 6 inputs. It des this by sending a packet f infrmatin at intervals. Between the intervals the transmitter is pwered dwn and the micrcntrller ges int sleep mde. The lnger the perid f sleep the greater the battery life will be. Mnths Battery Life Perid Secnds Figure 1 Apprximate battery life Cin AAA Fr a typical AAA cell (3 wuld be needed fr 4.5V) the battery life varies frm abut 2 mnths fr the shrtest perid, 1 secnd t nearly 2 years fr a 2 minute perid. The device will wrk frm 3V and s tw cells will wrk but this des nt give any margin as the cells becme depleted. August f 5

3 Prduct Specificatin 5. Blck Diagram 1 at the tp f the bard t 8 at the bttm, the antenna is pin 9, tp left Pwer (+v) Pwer t the bard can be prvided by a battery the vltage shuld be in the range 3 t 5.5V. Three cells are ideal Grund Grund (GND) Figure 2 Blck Diagram The prcessr accepts the inputs frm the 2 analgue channels which are cnverted t ten bit numbers. This is then transmitted as a packet. The packet has an address and this can be changed by the user. The packet will be a cpy f the data at the inputs. An aerial can be fitted t the ANT f the transmitter fr increased range. In practice a piece f wire 160mm lng wrks kay, this is the length f the ¼ wave. 6. External Cnnectin Figure 3 Physical Layut f Cnnectrs 6.3. PO This pin is used fr external sensrs and will prvide a pwer supply frm the battery f up t 150mA, pulsed at the rate set by the address. The purpse being that the external devices (a temperature sensr fr example) are nly pwered up when required. The pwer t this pin is available fr 30mS befre the vltage is sampled at either AD0 r AD1, this gives time fr the cnnected device t settle Vref This is the reference fr the analgue channels and effectively determines what vltage will be represented by the value f If this pin is cnnected t a 3V reference then when either pin AD0 r AD1 reached 3V the value utput will be Fr battery perated equipment a reference shuld be used. This can be pwered frm the PO pin t save pwer. An external LED culd als be used, fr lw accuracy applicatins, as a reference at pin 7 as the frward vltage drp will be apprximately 2 vlts but this will vary slightly as the battery vltage changes. A final alternative wuld be t simply cnnect vref t +V Analgue Channels There are tw10 bit analgue channels AD0 and AD1, 10 bits will give a range f 0 t 1023, every time a packet is transmitted the value f bth channels will be cntained within the packet at each transmissin perid LED The LED is supplied frm the pwer switch that the prcessr peridically switches n (P0). There is als an utput fr an external LED that has a 2k7 series resistr n bard. The Ande shuld be cnnected t pin 7. The LED illuminatin indicates that a packet is being sent. Figure 4 Circuit Symbl The interface is via 8 pads at the right hand edge f the bard, the pads are numbered frm 7. Packet Descriptin The packet is a series f bytes sent as a single message. The general frmat is: ByVac Page 3 f 5

4 Prduct Specificatin <preamble><length><address><analgue><c hecksum> P L A AD0 AD1 C Nt that is a BV4116/7 is used then the preamble, checksum and length calculatins are all taken care f. Preamble (4 bytes) The preamble is t help synchrnise the receiver and cnsist f three bytes with a value f 0x22 fllwed by ne byte with a value f 2 Length (8 bits) The length byte will always have a value f 6 meaning 6 bytes fllw including the checksum. Address (8 bits) Fr this particular device the address and paylad have definite values, fr addressing see the sectin n addressing, this can have a value frm 1 t 8 Analgue channels (16 bits each) The analgue channel reflects the value fr the A t D cnversin. This 16 bit value will vary frm 0 t 1023 depending n the vltage n the channel and at Vref. There is ne 16bit wrd transmitted fr each channel. Check Sum (8 bits) The checksum is generated by the prcessr frm all f the previus data, the receivers designed t wrk with this device will nt accept a packet with a faulty checksum. Packets can be read with a suitable receiver, these are BV4116 r BV Addressing & Perids As previusly described the time perid that the packet is transmitted can be varied frm apprximately 1 secnd t 2 minutes. This has an effect n battery life at the trade f pssibly missing inputs, hwever depending n the applicatin this may nt be imprtant. The address f the packet is directly related t the perid as fllws: Address Perid Secnds Apprximately The packet transmit perids is apprximate and the address refers t the address f the packet, nt the frequency f the transmitter which is fixed Setting the Address By default the device is set t address 1 but this can be changed by using the push buttn. The perid interval is given by the flashing LED, each time the LED flashes, a packet is transmitted. The fllwing prcedure will change the address: 1. Remve the pwer 2. Hld dwn the push buttn and recnnect the pwer. 3. The LED will flash 3 times and then slwly flash, each slw flash is a change in address, when a cunt f 8 is reached, the led will flash 3 times and start frm address 1 again. 4. Release the buttn when the desired address has been selected. The address is stred in EEPROM and s will remain until the prcedure abve is carried ut nce mre. 9. Temperature Sender Example The fllwing is a temperature sender using the lw cst LM35DZ, this will utput a vltage prprtinal t the temperature. The device perates frm 4V t 30 V s a supply vltage f at least 4V is required. Figure 5 Temperature Sender The pwer supply fr the LM35 is taken frm the PO pin, this means that the LM35 will nly be pwered up when it is needed. The utput is fed t channel A and channel B is nt used. Vref. is taken frm the cathde f a vltage reference dide, this will set Vref at abut 1.2V depending n the value fr the reference dide. The pwer supply is either 3 buttn (1.5V) cells r 3 AAA type cells, bth will give 4.5V with full capacity which is ideal. Three r fur rechargeable cells wuld als d, giving 3.6 and 4.8V respectively. Given this set up there will be an analgue value transmitted in the packet that represents the temperature. The LM32 will utput 10mV fr ByVac Page 4 f 5

5 Prduct Specificatin each degree C, s fr 21 degrees the utput will be 0.21mV. If the reference vltage is 1.2V then 1.2V equals a value at the Aa channel f 1023, s each value is 1.2V / 1023 = 0.002V, therefre at 21 deg. C the value expected wuld be: 0.21 / = 175 Or t put it a better way: Temperature in degrees C = A x 0.12 Where A is the analgue value at channel A. 10. Receiving The packets can be received by any suitable receiver mdule hwever the BV4116 (TX) r BV4117 (TX/RX) take much f the wrk ut f receiving the packets. When ne f these receivers are used the packet received is 5 bytes as fllws: <age><ad0><ad1> The age byte is used t indicate when the last packet was received. Tw bytes are used fr each f the AD0 and AD1 signals and the values reflect the vltage n the channel at the time the packet was transmitted. Fr mre infrmatin see the dcumentatin fr the BV4116/7. ByVac Page 5 f 5