Here’s a copy of the first thoughts put on paper
- Form factor: Raspberry Pi Hat (with screws places for both Raspberry Pi 3 and Raspberry Pi 0)
- Have the Oled, ADC, TGC, HV, Pulser, capa touch parts clearly separated (rectangle silkcreen + names)
- Ideally, rectangles with the different functions as defined on a block diagram, over the 6 items above.
- ADCs: both a 10-12 bit ADC (possibly from 10 to 30Msps – like the AD9200 is offering) - the other ADC being the SPI ADC (possibly AD7274) - to go up to 2 or 3 Msps, data being sampled is the enveloppe.
- Layers: 4 layers, if possible to have the RF noise as low as possible
- Components: easily sourcable in MacroFab (eg: initial transformer on goblin is not easy to find)
- Raspberry Pi headers connections as per details below
- Keeping room for the the 0.96” OLED screen variant on the top of the board for quick display + debug
- Jumper to select SPI ADC (goblin) or 10-12 bit 10Msps+ ADC (onboard - that can work at 10Msps up to 30Msps)
- Only 10 MSPS+ 10-12bit ADC. The faster ADC, like AD9629 costs approximately the same, but more complicated in use (SPI configuration, diff clock, 1.8V supply etc)
- If 10Msps ADC:
- Jumper to select Raw Signal or Enveloppe . If RawSignal, to be offset by Vref/2.
- If SPI ADC:
- Only Enveloppe
- no need for variable Vref… as gain can be controlled beforehand.
- Jumper to select signal input to RPin (either from Enveloppe or RawSig).. or not
- Ideally, the two ADCs can be shut down, and signal only routed to RPin - in case the interleaved ADCs extension board is used.
TGC (ex goblin board)
- MD0100 or equivalent for protection of VGC
- Jumper : to select gain (3 choices)
- from pot (as per goblin)
- from external (0 to 1V - connected to the 6x2 header Gain) as per goblin
- or from an available pin from the 2x20 header
- Transfo: replace with one easily sourced from digikey / macrofab :)
HV (ex tobo board)
- Jumper: Selectable 0, 25, 50 or 75V
Pulser (ex tobo board)
- Unipolar, only with Pon and Poff (routed to 2x20 Raspberry header)
- Jumper: route pulse either to SMA or to “artificial” piezo (see RLC) that can stand the pulses.
- RLC : see for example http://www.brl.uiuc.edu/Downloads/bigelow/APPENDIX%20C.PDF
- or http://www.biosono.com/PrmtLgd/PrmtLgd.php?id=TrnsRlc with .. see below!
- One 6x2 header for add-ons (Pon, Poff, 5V, 3.3V, TGC Gain, Touch Interrupt, Trig, GND, SDA, SCL, PWM, Tracker). Silkscreen for the different items
- Power-on LEDs on the 3.3V line and 5V lines
- Would be good to have an onboard miniusb plug for easy power supply
- The board needs 2 or 3 touch-pad like zones, to be connected to i2c bus + 1 interrupt pin for detection of touching this zones, for controls (single acq, controls, settings, …)
!! Beware -> the ADC here has 14 bits, 12 is enough. In this case, 2 pins can be shifted to a “trig” pin + one to a gain pin