Photo-gate timer: Difference between revisions
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===Components=== | ===Components=== | ||
*Photogates | *Photogates | ||
**LED, infrared (~$0.20). I use a Lite-On LTE-302-M, which has a black dot to identify itself as an emitter; it also allows up to 50mA of current, so it can be used at a greater distance than 20mA emitters. | **LED, infrared (~$0.20). I use a Lite-On LTE-302-M, which has a black dot to identify itself as an emitter; it also allows up to 50mA of current, so it can be used at a greater distance than 20mA emitters. The cathode is the short lead, on the left as you're facing the lens. | ||
**Phototransistor, infrared (~$0.20). I use a Lite-On LTR-301, which has a red dot to identify itself as a receiver. | **Phototransistor, infrared (~$0.20). I use a Lite-On LTR-301, which has a red dot to identify itself as a receiver. The collector is the long lead, on the right as you're facing the lens, the short lead being the emitter of the transistor. | ||
**Switching transistor, 2N2222 or equivalent NPN (~$0.10) | **Switching transistor, 2N2222 or equivalent NPN (~$0.10) | ||
**Resistors | **Resistors | ||
Revision as of 12:27, 9 March 2014
Specifications
- Run on a battery.
- Include a multi-character display, at least four digits.
- Include a power switch to save the battery.
- Use a breadboard so it can be modified.
- Timing of periods of at least 10 s accurate to 0.01s
Circuit
Components
- Photogates
- LED, infrared (~$0.20). I use a Lite-On LTE-302-M, which has a black dot to identify itself as an emitter; it also allows up to 50mA of current, so it can be used at a greater distance than 20mA emitters. The cathode is the short lead, on the left as you're facing the lens.
- Phototransistor, infrared (~$0.20). I use a Lite-On LTR-301, which has a red dot to identify itself as a receiver. The collector is the long lead, on the right as you're facing the lens, the short lead being the emitter of the transistor.
- Switching transistor, 2N2222 or equivalent NPN (~$0.10)
- Resistors
- LED limiting resistor (~100Ω) (~$0.02)
- Phototransistor resistor (~5kΩ) (~$0.02)
- NPN base resistor (~50kΩ) (~$0.02)
- NPN collector resistor (~1kΩ) (~$0.02)
- Breadboard (~$5)
- Micro-controller ($2-$10)
- Power circuit if necessary ($1)
- Resonator circuit if necessary (~$1)
- Display, serial capable ($10), or
- TTL-to-USB or TTL-to-serial for sharing data with computer ($18)
- Hook-up wires ($2)
Power supply
Using a 3V LCD display will require us to use one 3V coin cell or two AA or AAA batteries. Or, we could use a 5V phone charger with a set of enough diodes to bring the voltage down, or find a rarer 3V plug-in power supply.
Program
- Clear the display
- Loop.
- Watch for a break in the first gate. If so, reset counter and continue to next loop.
- Loop.
- increment a counter periodically. Use a period of 10ms or less.
- Watch for a break in the second gate. If so, continue to the next section.
- Convert the counter to a proper number, if necessary.
- Display the number
- Return to the idling loop.
Datasheets
- Newhaven Display liquid crystal display module, with side white backlight and transflective display.
- http://www.newhavendisplay.com/specs/NHD-C0216CiZ-FSW-FBW-3V3.pdf
