Pololu-Romi-32U4-Carte-Alimentation
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Introduction
The Romi 32U4 Control Board includes battery terminal connections that provide access to power from the Romi chassis’s six-AA battery compartment. We recommend using rechargeable AA NiMH cells, which results in a nominal voltage of 7.2 V (1.2 V per cell). You can also use alkaline cells, which would nominally give you 9 V.
The negative battery voltage is connected to GND. The positive battery voltage is designated VBAT. VBAT feeds into a reverse protection circuit and then a power switching circuit controlled by the on-board pushbutton or slide switch. The output of the power switching circuit is designated VSW.
VSW provides power to the motors through the on-board DRV8838 motor drivers, so the motors can only operate if the batteries are installed and the power switch circuit is on.
The reverse protected and switched battery voltage on VSW can be monitored through a voltage divider that is connected to analog pin 1 (PF6) by default. The divider outputs a voltage that is equal to one third of the battery voltage, which will be safely below the ATmega32U4’s maximum analog input voltage of 5 V as long as the battery voltage is less than 15 V (though the maximum voltage for the board is still limited to 10.8 V by the DRV8838 motor driver). The readBatteryMillivolts() function in the Romi32U4 library can be used to determine the battery voltage from this reading. The surface-mount jumper labeled “A1 = BATLEV” can be cut to disconnect the voltage divider and free the pin for other uses.
Power switch circuit
The Romi 32U4 Control Board uses the patented latching circuit from the Pololu pushbutton power switch lien pololu, which provides a solid-state power switch for your robot controlled with the on-board pushbutton. By default, this pushbutton can be used to toggle power: one push turns on power and another turns it off. Alternatively, a separate pushbutton can be connected to the PWRA and PWRB pins and used instead. Multiple pushbuttons can be wired in parallel for multiple control points, and each of the parallel pushbuttons, including the one on the board itself, will be able to turn the switch on or off. The latching circuit performs some button debouncing, but pushbuttons with excessive bouncing (several ms) might not function well with it.
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For proper pushbutton operation, the board’s slide switch should be left in its Off position. (Sliding the switch to the On position will cause the board power to latch on, and the switch must be returned to the Off position before the board can be turned off with the pushbutton.) |
Alternatively, to disable the pushbutton, you can cut the button jumper labeled Btn Jmp; this transfers control of the board’s power to the on-board slide switch instead. A separate slide or toggle switch can be connected to the GATE pin and used instead.
The power switch circuit also offers several alternate pushbutton connection options that result in push-on-only or push-off-only operation, and additional inputs enable further power control options like allowing your robot to turn off its own power. These advanced control options are available through the button connection pins and four control inputs:
| Broche | Description |
| PWRA | Connect through momentary switch to pin “PWRB” for standard push-on/push-off operation. Connect through momentary switch to ground for on-only operation. |
| PWRB | Connect through momentary switch to pin “PWRA” for standard push-on/push-off operation. |
| ON | A high pulse (> 1 V) on this pin turns on the switch circuit. This pin only functions when pushbutton operation is enabled (i.e. the button jumper has not been cut). |
| OFF | A high pulse (> 1 V) on this pin turns off the switch circuit (e.g. allowing a powered device to shut off its own power). This pin only functions when pushbutton operation is enabled. |
| CTRL | With pushbutton operation enabled, this pin directly determines the state of the switch circuit. A high pulse (> 1 V) on this pin turns on the switch; a low pulse (e.g. driving the pin low with a microcontroller output line or pushing a button connected from this pin to ground) turns the switch off. Leave this pin disconnected or floating when not trying to set the switch state. Note that this pin should not be driven high at the same time the “OFF” pin is driven high. |
| GATE | With pushbutton operation disabled (button jumper cut), this pin controls the state of the switch circuit: driving it low turns the switch on, while letting it float turns the switch off. Connect through slide or toggle switch to ground for on/off operation. Leave this pin disconnected or floating for proper pushbutton operation. We recommend only ever driving this pin low or leaving it floating; this pin should never be driven high while the slide switch is in the “On” position. |
Régulateurs 5V et 3.3V
VSW supplies power to a 5 V regulator, whose output is designated VREG. The battery voltage is regulated to 5 V by an MP4423H switching buck converter; although the regulator itself works with input voltages up to 36 V, the motor drivers limit the control board’s maximum input voltage to 10.8 V. When available, VREG is generally used to supply logic power for the ATmega32U4, motor drivers, and encoders. The rest of the regulator’s achievable output current, which depends on input voltage and ambient conditions, can be used to power other devices; this can include an attached Raspberry Pi (which typically draws a few hundred milliamps). Under typical conditions, up to 2 A of current is available from the VREG output. (We also make a standalone regulator lien pololu based on this integrated circuit.)
The MP4423H regulator features an open-drain power good output, PG, which requires an external pull-up. PG drives low when the 5 V regulator’s output voltage falls below around 85% of the nominal voltage and becomes high-impedance when the output voltage rises above around 90%. The regulator circuit on the Romi 32U4 Control Board can be disabled by driving the regulator shutdown pin, REGSHDN, high; this will cause 5 V logic power for the control board to be sourced from USB instead if it is available.
The Romi 32U4 Control Board also contains a 3.3 V LDO that draws its power from the output of the logic power selection circuit described below. The output of the 3.3 V regulator is designated 3V3 and is used to supply the on-board inertial sensors and level shifters.
Basé sur "Guide utilisateur de la carte de contrôle Romi 32U4" de Pololu (https://www.pololu.com/docs/0J69) - Traduit en Français par shop.mchobby.be CC-BY-SA pour la traduction
Toute copie doit contenir ce crédit, lien vers cette page et la section "crédit de traduction". Traduit avec l'autorisation expresse de Pololu (www.pololu.com)
Based on "Pololu Romi 32U4 Control Board User’s Guide" from Pololu (https://www.pololu.com/docs/0J69) - Translated to French by shop.mchobby.be CC-BY-SA for the translation
Copies must includes this credit, link to this page and the section "crédit de traduction" (translation credit). Translated with the Pololu's authorization (www.pololu.com)