NEW PROTOTYPE: Logic Shrimp logic analyzer

The Logic Shrimp is a medium speed, low-cost logic analyzer with a USB interface. It can capture up to 256K samples at 20MHz, and is compatible with the open source SUMP logic analyzer client.

The 23K256 serial SRAM from Microchip makes this project possible. Each chip stores up to 256K samples from one logic analyzer channel. After demoing the SRAM at Hack a Day, Ian made a one channel logic probe with a single chip. The SCANALOGIC2 inspired this 4 channel version.

  • 4 channels @ 256K samples per channel
  • 5volt tolerant inputs
  • 20/12/6/3/2/1MHz capture rates, and lower
  • Simple edge change triggers on all channels, adjustable pre/post trigger samples
  • SUMP protocol compatible
  • USB interface, USB firmware upgradable
  • Open source (CC-BY-SA)

Hardware design overview

The Logic Shrimp design is diagrammed above. Four 23K256 SRAMs capture up to 256K samples on each channel. The SRAMs run at 3.3volts, but the Logic Shrimp inputs are 5volt tolerant thanks to a 74LVC573 buffer. A PIC 18F24J50 configures the SRAMs and provides a capture clock source: either from the pulse-width modulator, or from a 20MHz oscillator though a one-bit buffer.

Resources

You can get a Logic Shrimp for $34.90 only at Seeed Studio.


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3 Comments

  1. Thanks for that very clear hardware description writeup! It was easy to understand every part of the design. I do have to wonder if this item will be popular, given that your larger and more capable Logic Sniffer is only $15 more.

    1. We’re trying really hard not to go head to head with the Logic Sniffer. This was a fun design to explore and hopefully to read about. If someone buys one, great, but worst case we’ll give them all away as prizes :)

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