APRStt CONNECTIONS FOR THE DTMF chip to the LPT1 PORT 20 May 2002 ------------------------------------------------------------------------------ WB4APR This is the current schematic for the APRStt interface to the LPT1 port to both decode touchtones for APRStt off the air and to allow APRStt to speak back to the user. It does not curently implement the ability to send back DTMF to some of the older DTSS HT radios which will be a future enhancement. This design below uses the 5 available Input pins on the Parallel port and does NOT attempt to use the port as a bi-directional port which will not work on all PC's... I get 5 volts from the unused PS-2 keypboard socket on my laptop. The 8 output bits of the LPT1 port are used as a simple D/A converter to give APRStt its voice. Connections to the 8880 DTMF chip are: DB-25 LPT1 Port +-------+ *---*| |*---------------------*---> +5V 0.1 100k | | | 0.1 | Inpt --||--*--/\/\/\/--*| |*--------------*--||--+ | 100k | | | 390k | | +-----+ +--/\/\/\/--*| |*-----/\/\/\/--*------|--| XXX |--- Pin 15 | | | | +-----+ *---*| |*----- D3-------------|------------ Pin 11 | | | GND --------*| |*----- D2-------------|------------ Pin 10 | | | XTAL---*| |*----- D1-------------|------------ Pin 12 | | | XTAL---*| |*----- D0-------------|------------ Pin 13 | | 3.3k | DTMF OUT --------*| |*---------/\/\/\/-----+ | | | +5 R/W -------*| |* clock === 0.1 | | | not CS *---*| |*---* REG Sel | | +-------+ | | === === === = = = I/O PORT CONSIDERATIONS LPT1 PORT ADDRESS = 888 STATUS PORT ADDRESS = 889 BIT 8880 VAL DB25 color NAME OPEN out GND out note --- ---- --- ---- ----- ------ -------- ------- ----------- D7 D3 128 11 yel BUSY +5 0 1 HW inverted D6 D2 64 10 org nACK 0 1 0 defined inverted D5 D2 32 12 red Pempty +5 0 1 D4 D0 16 13 brn Select 0 0 0 D3 ESt 8 15 w nError +5 1 defined inverted D2 4 0 0 D2 2 0 0 D0 1 0 0 In software, to get the 8880 chip 4 bit outputs to read properly, 1) First XOR with 128 to reverse the Hardware inversion 2) Then binary divide by 16 to right shift the data. 3) Note that D3 is the state of the KEY press. It is 0 if no key and goes to 1 if there is a key pressed. Get this bit with AND 8 XXX CIRCUIT: This circuit unloads the digit-detect output and isolates it from the R/C time constant of the 390k and 0.1 uF cap. Then it is inverted an used to feed the Pin 15 to tell the APRStt that a new digit has been received. +5v-----------*----------------* |e | b|/ \ 10K >--/\/\/----|PNP / 470K |\ \ |c *------------> Pin 15 | |c | b|/ *---/\/\/\/----|NPN 100 K |\ |e === GND APRStt VOICE D/A CONVERTER USING THE LPT1 PORT ----------------------------------------------- +---------+ PIN-1 --------------------+ PTT CKT +----> To Radio PTT PIN-2 --<640K>--+ +---------+ PIN-3 --<320K>--+ PIN-4 --<160K>--+ PIN-5 --<80 K>--*---*---------||---------> To Radio Microphone input PIN-6 --<40 K>--+ \ 10uF PIN-7 --<20 K>--+ / PIN-8 --<10 K>--+ \ 33 Ohms PIN-9 --< 5 K>--+ / PIN-25--------------* PTT BUFFER CIRCUIT ------------------ This circuit converts the TTL level LPT1 Strobe bit to an open collector PTT output that should work with all radios... The 220k and 100 uF capacitor are a watchdog timer that will prevent the circuit from holding down PTT for longer than 22 seconds and the 10uF caps are to filter any noise from getting into the Mic circuit when PTT is combined with Mic audio on HT's. To combine PTT with Mic Audio, simply run the PTT output to the mic input through a 2.2k resistor. +---||---+ | 10uF | +--/\/\--*--------*--------------------> +5v | 220K | | | |e === 10 uF | b|/ | PIN-1 >--\/\/\--||--*------|PNP --- (strobe) 10K 100uF |\ /// GND |c *------------> PTT to Radio | |c | b|/ *---/\/\/\/----|NPN 2.2 K |\ |e === /// GND