TENSS AEMS

TENSS analog ephys measurement system

Through-hole PCB version of the full extracellular electrophysiology measurement system. INA121 instrumentation amplifier followed by an inverting active band-pass filter. Designed as a student soldering exercise: all parts are through-hole, the board is single-sided friendly, and the supply rails are decoupled with both bulk and HF caps for clean amplification of small extracellular signals.

Circuit overview

   J2.VIN+  ─┐                                      ┌─── J3.VOUT
            │   ┌─────────────┐    ┌────────────┐   │
            ├──►│  INA121P    ├───►│  LM358     ├───┤
            │   │  (U1)       │    │  band-pass │
   J2.VIN- ─┤   │  G≈2.06     │    │  (U2)      │
            │   │  Rg=47k     │    │  R1,R2,C1,C2│
            │   └─────────────┘    └────────────┘
   J2.REF  ─┘
                       ±V rails, REF, all decoupled to GND

The band-pass corners match the handout's spike-recording values.

Power decoupling

Every supply pin of each IC gets two caps to GND:

• 100 nF ceramic (C4, C6) — high-frequency bypass
• 10 µF electrolytic (C3, C5) — bulk reservoir for transients

Assembly notes for students

• Polarized parts: all "CP" capacitors (C3, C5) are electrolytic and must be installed with the long lead in the "+" hole. Reverse polarity = magic blue smoke (and possibly a small bang).
• ICs: the notch on the body of U1 and U2 must line up with the notch on the silkscreen outline. Pin 1 is the pin to the left of the notch when the notch is at the top.
• Power supply: ±9 V to ±15 V.
• Test before connecting electrodes: with power applied and the input shorted (VIN+ = VIN- = REF = GND), the output should sit at roughly 0 V. A large DC offset means something is wrong — most commonly a swapped electrolytic or a missed solder joint.