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author | Christian Starkjohann <cs+github@obdev.at> | 2008-04-17 19:00:20 +0000 |
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committer | Christian Starkjohann <cs+github@obdev.at> | 2008-04-17 19:00:20 +0000 |
commit | 95ca3f5bd696b5450820929e1b1a444d02f0bd1e (patch) | |
tree | 70ac0161a0e4548acaf2f89d2ecb77132579ff7a /circuits | |
parent | 2f465daef9e6c5a6b7bda3074c050cd7e8515770 (diff) | |
download | v-usb-95ca3f5bd696b5450820929e1b1a444d02f0bd1e.tar.gz v-usb-95ca3f5bd696b5450820929e1b1a444d02f0bd1e.tar.bz2 v-usb-95ca3f5bd696b5450820929e1b1a444d02f0bd1e.zip |
- imported new files into project
Diffstat (limited to 'circuits')
-rw-r--r-- | circuits/Readme.txt | 75 | ||||
-rw-r--r-- | circuits/tiny45-rc.sch | bin | 0 -> 193502 bytes | |||
-rw-r--r-- | circuits/with-series-diodes.sch | bin | 0 -> 213956 bytes | |||
-rw-r--r-- | circuits/with-vreg.sch | bin | 0 -> 215922 bytes | |||
-rw-r--r-- | circuits/with-zener.sch | bin | 0 -> 225561 bytes |
5 files changed, 75 insertions, 0 deletions
diff --git a/circuits/Readme.txt b/circuits/Readme.txt new file mode 100644 index 0000000..7b1a95d --- /dev/null +++ b/circuits/Readme.txt @@ -0,0 +1,75 @@ +This is the Readme file for the AVR-USB example circuits directory. + + +CIRCUITS IN THIS DIRECTORY +========================== +Since USB requires 3.3 V levels on D+ and D- but delivers a power supply of +ca. 5 V, some kind of level conversion must be performed. There are several +ways to implement this level conversion, see the example circuits below. + +with-vreg.png and with-vreg.sch (EAGLE schematics): + This circuit uses a low drop voltage regulator to reduce the USB supply to + 3.3 V. You MUST use a low drop regulator because standard regulators such + as the LM317 require at least ca. 2 V drop. The advantage of this approach + is that it comes closest to the voltage levels required by the USB + specification and that the circuit is powered from a regulated supply. If + no USB cable is used (connector directly soldered on PCB), you can even + omit the 68 Ohm series resistors. The disadvantage is that you may want to + use other chips in your design which require 5 V. Please check that the AVR + used in your design allows the chosen clock rate at 3.3 V. + +with-zener.png and with-zener.sch (EAGLE schematics): + This circuit enforces lower voltage levels on D+ and D- with zener diodes. + The zener diodes MUST be low power / low current types to ensure that the + 1k5 pull-up resistor on D- generates a voltage of well above 2.5 V (but + below 3.6 V). The advantage of this circuit is its simplicity and that the + circuit can be powered at 5 V (usually precise enough if the cable drop is + neglected). The disadvantage is that some zener diodes have a lower voltage + than 3 V when powered through 1k5 and the choice of components becomes + relevant. In addition to that, the power consumption during USB data + transfer is increased because the current is only limited by the 68 Ohm + series resistor. The zeners may even distort the signal waveforms due to + their capacity. + +with-series-diodes.png and with-series-diodes.sch (EAGLE schematics): + This is a simplified low-cost version of the voltage regulator approach. + Instead of using a voltage regulator, we reduce the voltage by the forward + voltage of two silicon diodes (roughly 1.4 V). This gives ca. 3.6 V which + is practically inside the allowed range. The big disadvantage is that the + supply is not regulated -- it even depends strongly on the power + consumption. This cannot be tolerated for analog circuits. + +tiny45-rc.png and tiny45-rc.sch (EAGLE schematics): + This is mostly an example for connecting an 8 pin device using the internal + RC oscillator for system clock. This example uses series diodes to limit + the supply, but you may choose any other method. Please note that you must + choose a clock rate of 16.5 MHz because only the receiver module for this + frequency has a PLL to allow higher clock rate tolerances. + + +GENERAL DESIGN NOTES +==================== +All examples have D+ on hardware interrupt INT0 because this is the highest +priority interrupt on AVRs. You may use other hardware interrupts (and +configure the options at the end of usbconfig.h accordingly) if you make sure +that no higher priority interrupt is used. + +Most examples have a 1M pull-down resistor at D+. This pull-up ensures that +in self-powered designs no interrupts occur while USB is not connected. You +may omit this resistor in bus-powered designs. Older examples had a pull-up +resistor instead. This is not compatible with the zener diode approach to +level conversion: 1M pull-up in conjunction with a 3.6 V zener diode give an +invalid logic level. + +All examples with ATMega8/88/168 have D+ at port D bit 2 (because this is +hardware interrupt 0) and D- on port D bit 4 because it is also a clock input +for timer/counter 0. This way the firmware can easily check for activity on +D- (USB frame pulses) by checking the counter value in regular intervals. If +no activity is found, the firmware should (according to the USB +specification) put the system into a low power suspend mode. + + + +---------------------------------------------------------------------------- +(c) 2008 by OBJECTIVE DEVELOPMENT Software GmbH. +http://www.obdev.at/ diff --git a/circuits/tiny45-rc.sch b/circuits/tiny45-rc.sch Binary files differnew file mode 100644 index 0000000..349f1ad --- /dev/null +++ b/circuits/tiny45-rc.sch diff --git a/circuits/with-series-diodes.sch b/circuits/with-series-diodes.sch Binary files differnew file mode 100644 index 0000000..d84d99e --- /dev/null +++ b/circuits/with-series-diodes.sch diff --git a/circuits/with-vreg.sch b/circuits/with-vreg.sch Binary files differnew file mode 100644 index 0000000..1f1797b --- /dev/null +++ b/circuits/with-vreg.sch diff --git a/circuits/with-zener.sch b/circuits/with-zener.sch Binary files differnew file mode 100644 index 0000000..e7da8e5 --- /dev/null +++ b/circuits/with-zener.sch |