SCREEN CALIPERS SERIAL HOW TO
SCREEN CALIPERS SERIAL SERIAL
SCREEN CALIPERS SERIAL SOFTWARE

Apply some plastic epoxy to the insulation and reinsert the wires. After verifying that you’re able to insert the insulated cable into the exit holes approximately 5mm, withdraw the wire till the bare wires are exposed. Using the ConnectorNoHandle print, place the 4 soldered conductors in the 1.5 mm on center cuts and use this as a guide to insert the wires into the connector with a handle. The goal is to be able to insert all 4 insulated conductors bonded together as shown in the picture. After cleaning up the print of Connector.stl, use a 1.5 mm drill bit to enlarge the exit holes and to remove any material in between. Apply solder to the first 15 mm of wire from the tip to stiffen the wire. Strip 20 mm of insulation off one end as shown in the pictures. This is the ubiquitous “jumper cable” product you get with Dupont connectors already attached.įor this connector you need 4 conductors, any color. Print both STLs at 0.1mm layer height, 20% infill, no support, with just a skirt, no brim (if you print with a brim it’s a pain to cleanup)įor wire I used 26AWG 1.27mm pitch flat cable. See below for a video of the prototype board in action. If you’re interested in building one, the board Gerber files are shared on. The schematic, software, and parts list are enclosed in the next step.

In fact all of the parts could be replaced with something else. The 1.5V regulator could be replaced by a AA battery. You could substitute a 2N7000 MOSFET in a TO-92 package for the BSS138. All of the chips except for the voltage regulator and MOSFET, are available in DIP packages. This could easily be built on a breadboard. The default on power up is mm, so it shouldn’t be much of an issue. For that you’d have to hack the caliper to simulate a button press on the units button. The only thing the board can’t do is set the mm/inches units being displayed on the caliper. To zero the caliper the board simply turns it off and on via a BSS138 N-channel MOSFET. For either type of connection to the host, the host can read the current value whenever it needs to.

SCREEN CALIPERS SERIAL SOFTWARE

The board is software configurable to output only when the value changes in the case of TTL serial, and for I2C an interrupt line goes high whenever the value changes and stays high till the host reads the current value. See CaliperUtils.cpp within the attached software.zip for the routine that unpacks the packet. The mcu reads one packet bit whenever the clock pin goes from high to low (vcc to 0V.) Each packet is composed of 24 bits. I chose the TLC3702 because it requires very few additional parts (just 2 resistors.)Īs long as the caliper has power applied to it, it will periodically send a packet of data representing the current value being displayed on the caliper. Note that there are lots of ways to level shift signals. The comparator’s vcc is set to the mcu’s vcc, so when the caliper signal value is at or above 0.75 the comparator shifts this to vcc, and when the caliper signal is below 0.75 the comparator shifts this to 0 volts. The comparator threshold for both signals is set to half the caliper voltage or 0.75 volts by way of a resistor voltage divider of the 1.5 volts output by the board’s AMS1117-1.5 LDO voltage regulator chip. To do that I use a TLC3702 comparator chip. These signals are at 1.5V and need to be level shifted to the mcu’s vcc.

The caliper data port has data and clock signals. The board’s vcc can be anywhere from 3 to 5 volts (although I’ve only tested it at 5V.)

SCREEN CALIPERS SERIAL HOW TO

I’ve designed a 3D printed connector for this purpose with detailed instructions below on how to make one. The connection to the caliper is made via the caliper’s data port. Through either interface you can perform several functions, such as zeroing the caliper, turning it on/off, getting the current reading, or receive notification only when a change occurs.

SCREEN CALIPERS SERIAL SERIAL

The board allows for either a TTL serial and/or an I2C interface. This board works with several models of inexpensive Chinese calipers and tire depth gauges. The PCB I designed is a caliper data interface.

Screen calipers serial