A conventional optical mouse uses a light emitting diode (LED) as the source of illumination for the optical mouse sensor. The next generation optical mouse uses a laser as the source of illumination for the optical mouse sensor. The nearly singular wavelength of laser light is capable of revealing much greater surface detail than the LED. Thus, the laser can track reliably even on tricky polished or wood-grain surfaces.
Along with the use of the laser light source come new challenges in the manufacturing of optical mice. Thus, what is needed is a method for manufacturing optical mice that accommodates the new laser light source.
In one embodiment of the invention, a method for programming a function of an optical mouse during assembly includes (1) mounting a dummy resistor on a printed circuit board, the dummy resistor being indicative of a parameter of the function, (2) mounting an optical mouse sensor and a nonvolatile memory on the printed circuit board, (3) coupling a laser to the optical mouse sensor to receive a drive current, (4) further assembling the optical mouse, and (5) after the further assembling the optical mouse, determining the parameter from the dummy resistor and programming the parameter into the nonvolatile memory. During startup of the optical mouse, the optical mouse sensor is programmed with the parameter from the nonvolatile memory and drives the laser accordingly.
In another embodiment of the invention, a method for programming a function of an optical mouse during assembly includes (1) mounting a resistor on a printed circuit board, the resistor being indicative of a parameter of the function, (2) mounting an optical mouse controller on the printed circuit board, the optical mouse controller being coupled to the resistor, (3) mounting an optical mouse sensor on the printed circuit board, (4) coupling a laser to the optical mouse sensor to receive a drive current. During startup of the optical mouse, the optical mouse controller senses the resistor and programs the parameter into the optical mouse sensor to drive the laser accordingly.
Use of the same reference numbers in different figures indicates similar or identical elements.
In one embodiment of the invention, vertical cavity surface-emitting lasers (VCSELs) are categorized by a bin number and a bin letter (e.g., 2A, 2B, 3A, and 3B). The bin number designates the current required for a laser to obtain a given output power. The bin letter designates the temperature coefficient of the drive current needed to keep the output power of a laser constant over temperature. For cost reasons, the individual lasers may not be marked with the bin designations. Instead, the lasers are separated into containers (e.g., bags, boxes, or trays) marked with the bin designations. One of the reasons that the lasers are sorted according to their drive conditions is so that their output power can be controlled accordingly for eye-safety purposes. Note that even if the lasers are individually marked, the marking may not be visible after the laser is assembled into the optical mouse.
The laser can be used as the illumination source for an optical mouse sensor in an optical mouse. The optical mouse sensor measures changes in position by optically acquiring sequential surface images and mathematically determining the direction and magnitude of movement. The optical mouse sensor also regulates the drive current to the laser.
In one embodiment of the invention, an appropriate resistor (hereafter “bin resistor”) is coupled to the optical mouse sensor to set the correct current range for the drive current. Furthermore, a register in the optical mouse sensor is written to set (1) the correct drive current within the current range and (2) the correct temperature coefficient for the drive current. Typically during the startup of the optical mouse, an optical mouse controller reads the drive current and temperature coefficient settings from a nonvolatile memory and writes the settings into the sensor register.
During assembly, a worker receives a container full of lasers. According to the bin number on the container, the assembly worker programs the pick and place equipment to place the appropriate bin resistor onto the printed circuit board of the optical mouse. Subsequently, additional assembly of the optical mouse occurs.
After largely assembling the optical mouse, an assembly worker programs the temperature coefficient setting into a nonvolatile memory on the printed circuit board. To do this, the assembly worker needs to know the bin letter of the laser in the optical mouse. However, this point of the assembly process can be physically and temporally removed from the initial step where the laser container and the bin designations are accessible.
If one assembly worker were to mark the printed circuit board with the bin letter, then another assembly worker could read this marking and type the information into the equipment that programs the nonvolatile memory. However, this would be inefficient and error prone. Since eye-safety limits are jeopardized by mistakes, this method is not desirable.
In step 102, surface mount components including a bin resistor 202 (
In step 104, one or more surface mount resistors 210 (only one is shown in
In one embodiment, tempco resistors 210 are zero-ohm resistors. For example, a single zero-ohm resistor can be used to indicate whether the temperature coefficient function of the optical mouse sensor is to be used or not. Alternatively, multiple zero-ohm resistors can be used to represent a binary code that indicates a specific temperature coefficient to be used by the optical mouse sensor. For example, with two pairs of probe contacts, one of four possible temperature coefficients can be designated.
In another embodiment, tempco resistors 210 have resistances selected to indicate the specific temperature coefficient to be used by the optical mouse sensor. Thus, there is a correspondence between specific resistance values and temperature coefficient settings.
After all the surface mount components are placed on printed circuit board 204, the assembly is passed through a reflow oven to solder these components to board 204.
In step 106, through-hole components including a laser 212 (
In step 108, additional steps for assembling optical mouse 200 are performed. For example, an adhesive film used to protect laser 212, controller 213, and sensor 214 from the soldering process is removed, printed circuit board 204 is joined with an optical element (e.g., a lens) and a bottom case, laser 212 on tab 204A is inserted into the optical element and held in place by a clip (at which point any bin letter marking on laser 212 becomes obscured), and laser 212 is electrically coupled to the main printed circuit board 204 (specifically sensor 214) by a flexible cable 218. Only at this point may optical mouse 200 be powered on and calibrated.
In step 110, the largely assembled optical mouse 200 is calibrated. For example, the calibration process involves measuring the optical power exiting optical mouse 200 through the optical element in a temperature controlled environment. The register of optical mouse sensor 214 is written to change the drive current setting and the calibration process is repeated until a drive current setting that achieves the desired optical power is determined. Note that the temperature coefficient of laser 212 is not be determined from the calibration process and must be known from the bin letter.
In step 112, calibration data (e.g., the drive current setting) and the temperature coefficient setting are programmed into nonvolatile memory 212. For the temperature coefficient setting, testing equipment can be used to sense the current or the resistance between the probe contacts and then automatically program the corresponding temperature coefficient setting into nonvolatile memory 212. Alternatively, an assembly worker can visually inspect the tempco resistors and then manually program the appropriate temperature coefficient setting into nonvolatile memory 212.
In step 302, surface mount components including programmable bin resistor 402 and controller 413 are placed on a printed circuit board 404 (
In step 304, one or more surface mount tempco resistors 410 are placed on printed circuit board 404 according to the bin letter marked on the laser container. Specifically, zero-ohm tempco resistors 410 can be placed on solder joints between respective traces 406 and rail Vdd (or ground) in a debugging area 409 (
As similarly described above, a single tempco resistor 410 can be used to indicate whether the temperature coefficient function of the optical mouse sensor is to be used or not. Alternatively, multiple tempco resistors 410 can be used to represent a binary code that indicates a specific temperature coefficient to be used by the optical mouse sensor.
In step 306, through-hole components including a laser 412 (
In step 308, additional steps for assembling optical mouse 400 are performed. Step 308 is similar to step 108 described above.
In step 310, the largely assembled optical mouse 400 is calibrated. Step 310 is similar to step 110 described above except that the drive current is varied by programming bin resistor 402 instead of sensor 414.
In step 312, the correct drive current setting is programmed into bin resistor 402.
The operation of optical mouse 400 is now explained. During startup, controller 413 senses the presence of tempco resistors 410 through traces 406 and then writes the corresponding temperature coefficient setting into the register of sensor 414. Sensor 414 then provides the appropriate drive current to laser 414 according to the resistance provided by bin resistor 402 and the temperature coefficient setting in the sensor register.
Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. Although the dummy resistors have been used to record a temperature coefficient of a laser in an optical mouse, the dummy resistors can be used to record other characteristics of other devices. Furthermore, surface mount components can be replaced with through-hole mount equivalents, and vice versa. Numerous embodiments are encompassed by the following claims.