DC motor – Experimental Engineering

Posted on February 22, 2018 by The Engineer — Leave a comment

Brother PT-E300 Industrial Label Machine Teardown

Here a tape is installed in the printer. This unit can handle tape widths up to 18mm. The pinch rollers are operated by the white lever at the top of the image, which engages with the back cover.

This printer is supplied with a rechargeable battery pack, but AA cells can be used as well. Some of the AA battery terminals can be seen above the battery.

Pretty standard fare for a 2-cell lithium pack. The charging circuitry doesn’t appear to charge it to full voltage though, most likely to get the most life from the pack.

With the cartridge removed, the printer components can be seen. As these cartridges have in effect two rolls, one fro the ribbon & one for the actual label, there are two drive points.

The thermal print head is hidden on the other side of the steel heatsink, while the pinch rollers are on the top right. The plastic piece above the print head heatsink has a matrix of switches that engage with holes in the top of the label cartridge, this is how the machine knows what size of ribbon is fitted.

Most of the internal space is taken up by the main board, with the microprocessor & it’s program flash ROM top & centre.

The charger input is located on the keyboard PCB just under the mainboard, which is centre negative, as opposed to 99% of other devices using centre positive, the bastards.

The dot-matrix LCD is attached to the mainboard with a short flex cable, and from the few connections, this is probably SPI or I²C.

The printer itself is driven by a simple DC motor, speed is regulated by a pair of photo-interrupters forming an encoder on the second gear in the train.

The back case has the battery connections for both the lithium pack & the AA cells, the lithium pack has a 3rd connection, probably for temperature sensing.

Posted on February 25, 2017April 24, 2017 by The Engineer — Leave a comment

IC Decap – TA7291 H-Bridge DC Motor Driver

Here’s a jellybean chip – a DC motor driver. This device has all the logic to drive a small motor, such as that used to drive the tray of a CD drive in both directions. The control logic is at the bottom of the die, while the main power transistors are at the top, in H-Bridge formation.

Posted on April 24, 2016 by The Engineer — Leave a comment

HP SureStore DAT40 Tape Drive

Magnetic tape is the medium of choice for my offline backups & archives, as it’s got an amazing level of durability when in storage. (LTO Has a 30 year archival rating).
For the smaller stuff, like backing up the web server this very site runs on, another format seemed to suit better. Above is a HP DDS4 tape drive, which will store up to 40GB on a cassette compressed.
I picked this format since I already had some tapes, so it made sense.

Here’s the info for those who want to know. It’s an older generation drive, mainly since the current generation of tape backup drives are hideously expensive, while the older ones are cheap & plentiful. Unfortunately the older generation of drives are all parallel SCSI, which can be a expensive & awkward to set up. Luckily I already have other parallel SCSI devices, so the support infrastructure for this drive was already in place.

On the bottom of the drive is a bank of DIP switches, according to the manual these are for setting the drive for various flavours of UNIX operating systems. However it doesn’t go into what they actually change.

The bottom of the drive has the control PCB. The large IC on the left is the SCSI interface, I’ve seen this exact same chip on other SCSI tape drives. Centre is a SoC, like so many of these, not much information available.

Removing the board doesn’t reveal much else, just the bottom of the frame with the tape spool motors on the right, capstan motor bottom centre. The bottom of the head drum motor is just peeping through the plastic top centre.

Here’s the head drum itself. These drives use a helical-scan flying head system, like old VHS tape decks. The top of the capstan motor is on the bottom right.

Hidden just under the tape transport frame is the head cleaning brush. I’m not sure exactly what this is made of, but it seems to be plastic.

A single small DC motor with a worm drive handles all tape loading tasks. The PCB to the bottom left of the motor holds several break-beam sensors that tell the drive what position the transport is in.

Here’s the overall tape transport. The PCB on top of the head drum is a novel idea: it’s sole purpose in life is to act as a substrate for solder blobs, used for balancing. As this drum spins at 11,400RPM when a DDS4 tape is in the drive, any slight imbalance would cause destructive vibration.

Here’s the drive active & writing a tape. (A daily backup of this web server actually). The green head cleaning brush can be better seen here. The drive constantly reads back what it writes to the tape, and if it detects an error, applies this brush momentarily to the drum to clean any shed oxide off the heads. The tape itself is threaded over all the guides, around the drum, then through the capstan & pinch roller.