Source: https://guthlabs.ai/docs/instruments/schmitt-trigger-threshold-calculator/
instrument / verified-with-binding-errata
# Schmitt Trigger Threshold Calculator
The current ledger marks this instrument verified with errata that must be applied at binding time.
Status: **VERIFIED_WITH_ERRATA**Lifecycle: **verified-with-binding-errata**
## Inspectable records
[01**Overview**Purpose and lifecycle]()[02**Mechanism**Method and assumptions]()[03**Implementation**Binding and validation]()[04**Qualification**Evidence and errata]()
## Ledger state
The current ledger marks this instrument verified with errata that must be applied at binding time.
**Area**: Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab
**Tranche**: tranche-5
**Evidence ID**: t5-189
**Ledger rows**: 1
No ledger note is attached.
## Review findings
The instrument cannot honestly claim to compute general op-amp Schmitt-trigger upper and lower trip points until the topology, resistor placement, reference voltage, and positive/negative saturation definitions are specified. The provided vectors use the additional symmetric zero-reference assumption. The original second-vector value was corrected in the working and expected outputs to maintain arithmetic accuracy.
### Formula and scope findings
- VTH=Vsat×R1/(R1+R2) is valid only for a specific zero-reference Schmitt-trigger topology and resistor placement; it is not a universal op-amp Schmitt-trigger threshold formula.
- The specification does not define the reference configuration, so VTH+ and VTH− cannot be uniquely determined. A nonzero reference voltage changes both thresholds.
- Only one Vsat is provided, but real circuits may have unequal positive and negative saturation levels. The formula must specify whether Vsat is a positive magnitude, a signed rail, or separate Vsat+ and Vsat− values.
- hysteresis=VTH_high−VTH_low is standard, but VTH_high and VTH_low are not independently defined by the supplied formula. For a symmetric zero-reference circuit, the result would be 2×Vsat×R1/(R1+R2).
### Unit assumptions
- Vsat is treated as a positive voltage magnitude in volts.
- R1 and R2 must use the same resistance unit; only their ratio matters.
- The test-vector calculations assume a zero-reference, symmetric Schmitt-trigger configuration in which VTH+=+Vsat×R1/(R1+R2) and VTH−=−Vsat×R1/(R1+R2).
- Positive resistance values are assumed unless explicitly testing a boundary case.
## Boundary hardening
**BREAK_CLAIMED** · SELF_FLAGGED
The denominator can be forced to zero with R1+R2=0, producing an undefined threshold that must be rejected. In addition, the specification provides only one threshold formula and does not explicitly define how VTH_plus and VTH_minus, reference polarity, or signed hysteresis are derived.
## Errata and corrections
### Tranche errata
**VTH_plus/minus/hysteresis** · vector 2
±9.4737 / 18.947
±9.8947 / 19.789
outputs contradict her own working which computes (and self-corrects to) 9.8947
## Inspectable example
4 review vectors are recorded. One source-bound sample is shown below.
````
{
"inputs": {
"Vsat": 5,
"R1": 10000,
"R2": 20000,
"reference_config": "zero reference; symmetric rails; R1 and R2 in ohms"
},
"expected_outputs": {
"VTH_plus": 1.6666666667,
"VTH_minus": -1.6666666667,
"hysteresis": 3.3333333333
},
"working": "R1+R2=10000+20000=30000 ohms. VTH magnitude=5×10000/30000=50000/30000=1.6666666667 V. VTH+=+1.6666666667 V. VTH−=−1.6666666667 V. Hysteresis=VTH+−VTH−=1.6666666667−(−1.6666666667)=3.3333333333 V."
}
````
## Related workflows
No source-defined multi-instrument workflow membership is recorded.
## Sources and evidence
These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.
- `VERIFIED_LEDGER.json · VERIFIED_WITH_ERRATA`
- `evidence-tranche5/tranche5-results.json`
- `BOUNDARY_HAZARD_CATALOG.json`