I'm trying to spoof a 433 MHz remote and I have a sequence of 32 bytes that I want to repeatedly shift out to one of ATtiny85's pins. The signal then goes to a cheap Chinese-type 433 Mhz transmitter.
I utilized the built-in 8-bit Timer/Counter0. Unfortunately, in constant places in my sequence there are glitches in form of repeated bits.
For example (byte no. 5):
Bit number (starting from 0) 40 41 42 43 44 45 46 47
Correct 0 0 1 0 0 1 0 0
Actual 0 0 0 1 0 0 1 0
My code:
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#define OUT PB2
uint8_t bit = 0; // current bit
const uint8_t data[32] PROGMEM = {
0b10101010,
0b10101010,
0b10101010,
0b00000000,
0b01001001,
0b00100100,
0b11010011,
0b01101101,
0b00110100,
0b10010011,
0b01001101,
0b10100110,
0b11010010,
0b01001101,
0b10100100,
0b10011010,
0b01101001,
0b10110110,
0b10011010,
0b01101101,
0b10110100,
0b11011011,
0b01101101,
0b10110110,
0b11011010,
0b01101101,
0b10110100,
0b11011010,
0b01101000,
0b00000000,
0b00000000,
0b00000000,
};
int main() {
DDRB |= _BV(OUT);
TCCR0A |= _BV(WGM01); // clear timer on compare match
TIMSK |= _BV(OCIE0A);
// 2 kbps
TCCR0B |= _BV(CS01); // prescaler: 8
OCR0A = 62; // timer counts to 62 instead of 255
sei();
while (1) { }
}
ISR (TIMER0_COMPA_vect) {
if (pgm_read_byte(&(data[bit / 8])) & (1 << bit % 8)) { // read current bit from progmem array
PORTB |= _BV(OUT);
} else {
PORTB &= ~_BV(OUT);
}
// I tried
// if (bit == 255) bit = 0; else bit++;
// but it made no difference, so i left it like this
// because it's shorter
bit++; // let it overflow
}
I wondered if somebody could help me to troubleshoot this or maybe propose a better solution to this task which is just shifting out bytes without a clock.
EDIT: A comparison between "measured" and correct sequence (always the same, even after looping many times)
Bit Correct Measured
0 1 1
1 0 0
2 1 1
3 0 0
4 1 1
5 0 0
6 1 1
7 0 0
8 1 1
9 0 0
10 1 1
11 0 0
12 1 1
13 0 0
14 1 1
15 0 0
16 1 1
17 0 0
18 1 1
19 0 0
20 1 1
21 0 0
22 1 1
23 0 0
24 0 0
25 0 0
26 0 0
27 0 0
28 0 0
29 0 0
30 0 0
31 0 1 DIFFERENT
32 0 0
33 1 0 DIFFERENT
34 0 1 DIFFERENT
35 0 0
36 1 0 DIFFERENT
37 0 1 DIFFERENT
38 0 0
39 1 0 DIFFERENT
40 0 0
41 0 1 DIFFERENT
42 1 0 DIFFERENT
43 0 0
44 0 1 DIFFERENT
45 1 0 DIFFERENT
46 0 0
47 0 1 DIFFERENT
48 1 1
49 1 0 DIFFERENT
50 0 0
51 1 1
52 0 0
53 0 1 DIFFERENT
54 1 1
55 1 1
56 0 0
57 1 1
58 1 1
59 0 0
60 1 1
61 1 1
62 0 0
63 1 0 DIFFERENT
64 0 0
65 0 1 DIFFERENT
66 1 0 DIFFERENT
67 1 1
68 0 1 DIFFERENT
69 1 0 DIFFERENT
70 0 0
71 0 1 DIFFERENT
72 1 1
73 0 0
74 0 0
75 1 1
76 0 0
77 0 0
78 1 1
79 1 1
80 0 0
81 1 1
82 0 1 DIFFERENT
83 0 0
84 1 0 DIFFERENT
85 1 1
86 0 0
87 1 0 DIFFERENT
88 1 1
89 0 1 DIFFERENT
90 1 0 DIFFERENT
91 0 0
92 0 1 DIFFERENT
93 1 0 DIFFERENT
94 1 1
95 0 0
96 1 1
97 1 0 DIFFERENT
98 0 0
99 1 1
100 0 0
101 0 1 DIFFERENT
102 1 1
103 0 1 DIFFERENT
104 0 0
105 1 1
106 0 1 DIFFERENT
107 0 0
108 1 0 DIFFERENT
109 1 1
110 0 0
111 1 0 DIFFERENT
112 1 0 DIFFERENT
113 0 1 DIFFERENT
114 1 0 DIFFERENT
115 0 0
116 0 1 DIFFERENT
117 1 0 DIFFERENT
118 0 1 DIFFERENT
119 0 0
120 1 1
121 0 0
122 0 1 DIFFERENT
123 1 1
124 1 0 DIFFERENT
125 0 0
126 1 1
127 0 1 DIFFERENT
128 0 0
129 1 0 DIFFERENT
130 1 1
131 0 0
132 1 1
133 0 1 DIFFERENT
134 0 0
135 1 0 DIFFERENT
136 1 1
137 0 1 DIFFERENT
138 1 0 DIFFERENT
139 1 1
140 0 1 DIFFERENT
141 1 0 DIFFERENT
142 1 1
143 0 0
144 1 1
145 0 0
146 0 1 DIFFERENT
147 1 1
148 1 0 DIFFERENT
149 0 0
150 1 1
151 0 1 DIFFERENT
152 0 0
153 1 1
154 1 1
155 0 0
156 1 1
157 1 1
158 0 0
159 1 0 DIFFERENT
160 1 0 DIFFERENT
161 0 1 DIFFERENT
162 1 0 DIFFERENT
163 1 1
164 0 1 DIFFERENT
165 1 0 DIFFERENT
166 0 1 DIFFERENT
167 0 1 DIFFERENT
168 1 1
169 1 0 DIFFERENT
170 0 1 DIFFERENT
171 1 1
172 1 0 DIFFERENT
173 0 1 DIFFERENT
174 1 1
175 1 1
176 0 0
177 1 1
178 1 1
179 0 0
180 1 1
181 1 1
182 0 0
183 1 0 DIFFERENT
184 1 1
185 0 1 DIFFERENT
186 1 0 DIFFERENT
187 1 1
188 0 1 DIFFERENT
189 1 0 DIFFERENT
190 1 1
191 0 0
192 1 1
193 1 0 DIFFERENT
194 0 1 DIFFERENT
195 1 1
196 1 0 DIFFERENT
197 0 1 DIFFERENT
198 1 1
199 0 1 DIFFERENT
200 0 0
201 1 1
202 1 1
203 0 0
204 1 1
205 1 1
206 0 0
207 1 0 DIFFERENT
208 1 0 DIFFERENT
209 0 1 DIFFERENT
210 1 0 DIFFERENT
211 1 1
212 0 1 DIFFERENT
213 1 0 DIFFERENT
214 0 1 DIFFERENT
215 0 0
216 1 1
217 1 0 DIFFERENT
218 0 1 DIFFERENT
219 1 1
220 1 0 DIFFERENT
221 0 1 DIFFERENT
222 1 1
223 0 0
224 0 0
225 1 0 DIFFERENT
226 1 1
227 0 0
228 1 1
229 0 1 DIFFERENT
230 0 0
231 0 0
232 0 0
233 0 0
234 0 0
235 0 0
236 0 0
237 0 0
238 0 0
239 0 0
240 0 0
241 0 0
242 0 0
243 0 0
244 0 0
245 0 0
246 0 0
247 0 0
248 0 0
249 0 0
250 0 0
251 0 0
252 0 0
253 0 0
254 0 0
255 0 0
256 0