Drum unit capable of suppressing complication of wiring

1. A drum unit attachable to and detachable from an image forming apparatus, the drum unit comprising:

a photosensitive drum rotatable about a first axis extending in an axial direction;

a developing unit comprising:

a magnetic roller rotatable about a second axis extending in the axial direction, and configured to supply toner to the photosensitive drum;

a developer container accommodating therein carrier, and having an inlet;

a conveyer member positioned in the developer container, and configured to convey the toner and the carrier from the inlet toward the magnetic roller; and

a toner sensor configured to detect amount of toner in the developer container;

a toner cartridge accommodating therein toner and attachable to the developer container to replenish the toner in the developer container through the inlet;

a connector electrically connected to the image forming apparatus in response to attachment of the drum unit to the image forming apparatus; and

a relay board electrically connecting the toner sensor to the connector, the relay board being configured to transmit a detection signal from the toner sensor to the image forming apparatus.

2. The drum unit according to claim 1 , further comprising a toner memory provided on the toner cartridge, the toner memory being configured to store therein information related to the toner cartridge;

wherein the relay board electrically relays the connector and the toner memory to transmit the information stored in the toner memory to the image forming apparatus.

3. The drum unit according to claim 2 , wherein the relay board comprises a drum memory configured to store therein information related to the drum unit;

wherein the relay board is electrically connected to the connector to transmit the information on the drum memory to the image forming apparatus.

4. The drum unit according to claim 1 , wherein the developer container has one end portion in the axial direction where the inlet is positioned and has another end portion in the axial direction where the toner sensor is positioned.

5. The drum unit according to claim 1 , wherein the conveyer member comprises:

a first auger configured to convey the toner and the carrier in a direction from one end to another end in the axial direction of the developer container;

a second auger configured to convey the toner and the carrier in a direction from the another end to the one end of the developer container.

6. The drum unit according to claim 1 , wherein the photosensitive drum comprises a set of a plurality of photosensitive drums;

wherein the developing unit comprises a set of a plurality of developing units, each developing unit comprising the toner sensor;

wherein each toner sensor is electrically connected to the relay board.

7. The drum unit according to claim 6 , further comprising a frame supporting the plurality of the photosensitive drums and the plurality of the developing units;

wherein the connector is positioned on an outer surface of the frame.

8. The drum unit according to claim 7 , wherein the relay board is provided on the frame;

wherein the toner cartridge comprises a set of a plurality of toner cartridges, each toner cartridge comprising a toner memory, each toner memory being configured to store therein information related to each toner cartridge,

the drum unit further comprising:

a plurality of first electrical contacts positioned at an inner surface of the frame, each first electrical contact being electrically connectable to each toner memory;

a plurality of second electrical contacts positioned at an inner surface of the frame, each second electrical contact being electrically connected to each toner sensor;

a first cable connecting the relay board to the first electrical contacts and the second electrical contacts; and

a second cable connecting the relay board to the connector.

9. The drum unit according to claim 1 , wherein the toner sensor is a magnetic sensor configured to detect magnetic permeability.