I have a CHQ 1838 IR receiver. When the Arduino Uno receives an unknown code and re-sends it raw, something triggers the receiver again. (When a known code is received, re-sending doesn't trigger the receiver.) I thought it was light from the IR LED, but I by-passed the IR LED and the receiver is still triggered. If I disconnect the output circuit completely, no problem. The IR LED is connected through a 2N3904 transistor.
So...electrical noise from the output circuit feeding back into the receiver?
The receiver has a 10k resistor between Vcc and the Out pin.
Notice where the following reads "Sent raw" then "Received unknown code, saving as raw" immediately after.
Received unknown code, saving as raw
Decoded Unknown(0): Value:0 (0 bits)
Raw samples(100): Gap:23848
Head: m3350 s1800
0:m350 s500 1:m350 s1400 2:m300 s550 3:m300 s550
4:m300 s550 5:m300 s550 6:m300 s550 7:m300 s550
8:m300 s550 9:m350 s500 10:m350 s500 11:m350 s550
12:m300 s550 13:m300 s1400 14:m300 s550 15:m300 s550
16:m300 s550 17:m300 s550 18:m300 s550 19:m350 s500
20:m350 s550 21:m300 s550 22:m300 s550 23:m300 s1400
24:m300 s550 25:m300 s550 26:m300 s550 27:m300 s550
28:m350 s500 29:m350 s500 30:m350 s550 31:m300 s550
32:m300 s550 33:m300 s550 34:m300 s550 35:m300 s550
36:m300 s550 37:m300 s1400 38:m300 s550 39:m350 s500
40:m350 s550 41:m300 s550 42:m300 s550 43:m300 s550
44:m300 s550 45:m300 s1400 46:m300 s550 47:m300 s1400
48:m350
Extent=51650
Mark min:300 max:350
Space min:500 max:1400
Sent raw
Received unknown code, saving as raw
Decoded Unknown(0): Value:0 (0 bits)
Raw samples(2): Gap:57862
Head: m50 s1800
Extent=1850
Mark min:32767 max:0
Space min:32767 max:0
Sent raw