DropBotV3Dev
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This page provides an overview of the new hardware development, broken down into sub-tasks.
To reduce system cost, we plan to transition to DC switching (transistors or a HV ASIC) instead of using expensive AC PhotoMOS relays, which cost ~$5/channel. Ideally, we'd like to find: (a) an inexpensive ASIC with (b) a large number of channels that is (c) capable of switching voltages >200 V at (d) frequencies of >10 kHz. Our first candidate chip is HV507, which costs ~$20 in small quantities.
* Output voltage: 60-300 V (DC)
* HV supply current (all pins high, 300V): 0.5mA
* Max current per pin? (how is this defined for a capacitive load?)
* Max current total? (how is this defined for a capacitive load?)
We designed a PCB to test the HV507 chip (KiCad files on github). The PCB takes a HV input and breaks out all control pins to a 5x2 header (which we will connect to an Arduino to test). The HV outputs are connected to pogo pins that are compatible with the standard !DropBot connector (one PCB can be connected to each side of the device, but it looks like the connector will need to be modified a bit to allow clearance on one of the sides).
We connected an 80V source to the HV pin and toggled all pins with an Arduino (sketch), verifying that all pins worked with an oscilloscope.
* HV507 product page
* Arduino SPI reference
* KiCad files
Build a proto board (based on the Extension Module Proto Board) that can control two HV507 PCBs (from 1a with 10-pin ribbon cables.
* 64 bits x 2 (to switch on/off) = 128 bits/period
* 8 MHz SPI: 8e6 bits/second / (128 bits/period) = 62.5 kHz (64-channels)
* 4 MHz SPI: 4e6 bits/second / (128 bits/period) = 31.25 kHz (64-channels)
* 2 MHz SPI: 2e6 bits/second / (128 bits/period) = 15.6 kHz (64-channels)
How fast is shiftOutFast?
The HV switching module described above will need a power source. Ideally, this would be something that could be powered from 5-12V (or potentially from USB or a battery). Our first prototype will be based off a well known Nixie power supply (the same design used by the OpenDrop).
The output voltage of the boost converter is currently set by turning a potentiometer screw. We would like to modify this circuit to provide digital control (e.g., though a digital potentiometer). We can test this by soldering wires to the board and connecting them to a breadboard circuit + Arduino.
* Sept. 21, 2015 - 1a. Demonstrated toggling of switches between 0 and 80 V.