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[PCF7931] added IIR filter

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different tags seem to behave differently.
an old tag from the car had way worse signal. Therefore filtering made it way better.
Still not ideal.
This commit is contained in:
tinooo 2025-03-12 16:37:46 +01:00 • committed by Tino
commit 23ddf69f70
1 changed files with 19 additions and 9 deletions
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24
armsrc/pcf7931.c
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@ -28,6 +28,13 @@
#define T0_PCF 8 //period for the pcf7931 in us #define T0_PCF 8 //period for the pcf7931 in us
#define ALLOC 16 #define ALLOC 16
// IIR filter consts
#define IIR_CONST1 0.1f
#define IIR_CONST2 0.9f
// theshold for recognition of positive/negative slope
#define THRESHOLD 80
size_t DemodPCF7931(uint8_t **outBlocks, bool ledcontrol) { size_t DemodPCF7931(uint8_t **outBlocks, bool ledcontrol) {
const uint8_t DECIMATION = 4; const uint8_t DECIMATION = 4;
uint8_t bits[256] = {0x00}; uint8_t bits[256] = {0x00};
@ -70,7 +77,6 @@ size_t DemodPCF7931(uint8_t **outBlocks, bool ledcontrol) {
uint8_t block_done; uint8_t block_done;
size_t num_blocks = 0; size_t num_blocks = 0;
uint8_t threshold = 50; // threshold to filter out noise, from an actual edge.
EdgeType expectedNextEdge = FALLING; // direction in which the next edge is expected should go. EdgeType expectedNextEdge = FALLING; // direction in which the next edge is expected should go.
half_switch = 0; half_switch = 0;
@ -79,14 +85,15 @@ size_t DemodPCF7931(uint8_t **outBlocks, bool ledcontrol) {
bitPos = 0; bitPos = 0;
lastClockDuration=0; lastClockDuration=0;
for (sample = 1 ; sample < g_GraphTraceLen; sample++) { for (sample = 1 ; sample < g_GraphTraceLen-4; sample++) {
// condition is searching for the next edge, in the expected diretion. // condition is searching for the next edge, in the expected diretion.
if ( ((dest[sample] + threshold) < dest[sample-1] && expectedNextEdge == FALLING ) || //todo: without flouz
((dest[sample] - threshold) > dest[sample-1] && expectedNextEdge == RISING )) { dest[sample] = (uint8_t)(dest[sample-1] * IIR_CONST1 + dest[sample] * IIR_CONST2); // apply IIR filter
if ( ((dest[sample] + THRESHOLD) < dest[sample-1] && expectedNextEdge == FALLING ) ||
((dest[sample] - THRESHOLD) > dest[sample-1] && expectedNextEdge == RISING )) {
//okay, next falling/rising edge found //okay, next falling/rising edge found
expectedNextEdge = (expectedNextEdge == FALLING) ? RISING : FALLING; //toggle the next expected edge expectedNextEdge = (expectedNextEdge == FALLING) ? RISING : FALLING; //toggle the next expected edge
samplePosCurrentEdge = sample; samplePosCurrentEdge = sample;
beforeLastClockDuration = lastClockDuration; // save the previous clock duration for PMC recognition beforeLastClockDuration = lastClockDuration; // save the previous clock duration for PMC recognition
@ -146,7 +153,10 @@ size_t DemodPCF7931(uint8_t **outBlocks, bool ledcontrol) {
} else { } else {
// some Error. maybe check tolerances. // some Error. maybe check tolerances.
// likeley to happen in the first block. // likeley to happen in the first block.
Dbprintf(_RED_("ERROR in demodulation") " Length last clock: %d - check threshold/tolerance/signal. Toss block", lastClockDuration*DECIMATION);
// In an Ideal world, this can be enabled. However, if only bad antenna field, this print will flood the output
// and one might miss some "good" frames.
//Dbprintf(_RED_("ERROR in demodulation") " Length last clock: %d - check threshold/tolerance/signal. Toss block", lastClockDuration*DECIMATION);
// Toss this block. // Toss this block.
block_done = 1; block_done = 1;