USB IR Toy v1.1 update
From DP
Contents |
Development
- Design preview and discussion
- LED current calculation
- LED current calculation spreadsheet
- Another LED circuit
Prototypes
REV 4
REV 3
REV 2
REV1
Latest Schematic
Early schematic
Latest PCB
Early PCB
Partlist
| Part | Quantity | Value | Package |
|---|---|---|---|
| C1 | 1 | 0.1uf | C603 |
| C2,C4,C7 | 3 | 0.22uf | C603 |
| C5,C6 | 2 | 27pf | C603 |
| C8 | 1 | 1.0uF | C603 |
| D1 | 1 | SOD2514X100N | |
| D2,D3 | 2 | DO323 | |
| I | 1 | LED | CHIP-LED0805 |
| IC1 | 1 | PIC18F2550_28W | SO28W |
| ICSP | 1 | 1X05 | |
| J1 | 1 | CON-USB-MINI-BUSB1 | CONN_USB_MINI-B |
| JP1 | 1 | 2X06 | |
| Q1 | 1 | 20Mhz | HC49UP |
| R1 | 1 | 10k | R603 |
| R2 | 1 | 2K7 | R603 |
| R3,R6 | 2 | 390R | R603 |
| R4 | 1 | 7R | M1206 |
| R5 | 1 | 3K6 | R603 |
| RX | 1 | TSOP34838 | TSOP18XX |
| RX2 | 1 | QSE159 | QSE15X |
| S1 | 1 | SMD_TACT_SMALL | TACT_SWITCH_SMALL |
| T1 | 1 | BC81840MTF | SOT23-BEC |
| TX | 1 | 100mA IR LED | LED5MM |
| UART | 1 | 1X04 |
| Part | Value |
|---|---|
| C1 | 0.1uF capacitor (0805) |
| C2, C4, C7 | 0.22uF capacitor (0805) |
| C5,C6 | 27pF capacitor (0805) |
| C8 | 1.0uF capacitor (0805) |
| D1 | Small signal diode (DO323) |
| IC1 | PIC 18F2550-i/so (SOIC28W) |
| J1 | USB MINI-B jack (SMD) |
| Q1 | 20MHz crystal (SMD/HC49UP) |
| R1, R6 | 10,000 ohm resistor (0805) |
| R2 | 2700 ohm resistor (0805) |
| R3 | 390 ohm resistor (0805) |
| R4 | TX current limiting resistor, see table below (0805) |
| R5 | 1000 ohm resistor (0805) |
| T1 | NPN transistor, hfe 40+, 1A+ (SOT23) |
| I | indicator LED (0805) |
| RX | 5volt 38kHz IR receiver (eg: TSOP38238) |
| RX2 | QSE159 IR photosensor |
| TX | [60degree+ infrared emitter/LED] see table below (5mm) |
| Pin headers | 0.1" pin header (optional) |
| S1 | small tactile switch (optional) |
Transmitter circuit
We really want to get the transmitter section perfect on this version. Here's some optional LEDs:
Most IR LEDs seem to have a continuous current of 100mA and a pulse current of 200mA, and a voltage drop between 1.6 and 1.3.
- For 100mA - 39ohms, 0.34watts
- For 200mA - 18ohms, 0.68watts
Resistors
Most 0805 resistors are only good to .125 or .1 watts, so a way to have more power without a bigger resistor is to use more LEDs:
- For 100mA x 2 - 18R, 0.18watts
- For 100mA x 3 - 2R, 0.02watts
- For 200mA x 2 - 10R, 0.36watts
- For 200mA x 3 - 1R, 0.04watts
Another alternative is to use several resistors in parallel to increase the power rating. This should be cheaper - both in parts and board space.
Constant current
Calculations for a constant current LED driver. Spreadsheet.
Frequency measurement
