{"openapi":"3.1.0","info":{"title":"NTC Thermistor API","version":"1.0.0","description":"NTC-thermistor sensor maths as an API, computed locally and deterministically. The steinhart-hart endpoint converts between resistance and temperature using the Steinhart-Hart equation, 1/T = A + B·ln R + C·(ln R)³ — the most accurate NTC model — in both directions, solving the resistance at a given temperature with Cardano's cubic formula. The beta endpoint uses the simpler two-point Beta model, 1/T = 1/T0 + (1/β)·ln(R/R0) and R = R0·exp(β·(1/T − 1/T0)), to convert resistance to temperature or back from a reference resistance R0 at T0 (default 25 °C) and the beta coefficient. The divider endpoint recovers the thermistor's resistance from a voltage-divider reading — low-side R = Rs·Vout/(Vsupply − Vout) or high-side — so an ADC voltage can be turned into a resistance and then a temperature. Resistance is in ohms, temperature in °C (kelvin also returned), voltages in volts and beta in kelvin. Everything is computed locally and deterministically, so it is instant and private. Ideal for embedded, IoT, HVAC-control, 3D-printer and battery-management app developers, temperature-sensing and calibration tools, and electronics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is NTC thermistor conversion; for a generic resistive divider use an LED-resistor or voltage-drop API and for thermal expansion a thermal-expansion API.","contact":{"name":"PremiumApi","url":"https://www.oanor.com/by/premiumapi"}},"servers":[{"url":"https://api.oanor.com/thermistor-api","description":"oanor gateway"}],"tags":[{"name":"Thermistor"},{"name":"Meta"}],"components":{"securitySchemes":{"oanorKey":{"type":"apiKey","in":"header","name":"x-oanor-key","description":"Get your key at https://www.oanor.com/developer/keys"}}},"security":[{"oanorKey":[]}],"paths":{"/v1/beta":{"get":{"operationId":"get_v1_beta","tags":["Thermistor"],"summary":"Beta model","description":"","parameters":[{"name":"beta","in":"query","required":true,"description":"Beta coefficient (K)","schema":{"type":"string"},"example":"3950"},{"name":"r0","in":"query","required":true,"description":"Reference resistance R0 (Ω)","schema":{"type":"string"},"example":"10000"},{"name":"t0","in":"query","required":false,"description":"Reference temperature T0 (°C)","schema":{"type":"string"},"example":"25"},{"name":"resistance","in":"query","required":false,"description":"Resistance (Ω) for R→T","schema":{"type":"string"},"example":"6505"},{"name":"temperature","in":"query","required":false,"description":"Or temperature (°C) for T→R","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Beta model: 1/T = 1/T0 + (1/β)·ln(R/R0). Simple two-point fit; less accurate than Steinhart-Hart over wide ranges.","inputs":{"t0_c":25,"beta_k":3950,"r0_ohm":10000,"resistance_ohm":6505},"temperature_c":35.002,"temperature_k":308.152},"meta":{"timestamp":"2026-06-05T11:30:38.616Z","request_id":"04c6ff93-0560-4290-82d8-058ae0bbb2d9"},"status":"ok","message":"Beta model","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/divider":{"get":{"operationId":"get_v1_divider","tags":["Thermistor"],"summary":"Voltage divider","description":"","parameters":[{"name":"supply_voltage","in":"query","required":true,"description":"Supply voltage (V)","schema":{"type":"string"},"example":"3.3"},{"name":"output_voltage","in":"query","required":true,"description":"Midpoint voltage (V)","schema":{"type":"string"},"example":"1.5"},{"name":"series_resistor","in":"query","required":true,"description":"Series resistor (Ω)","schema":{"type":"string"},"example":"10000"},{"name":"side","in":"query","required":false,"description":"Thermistor side: low or high","schema":{"type":"string"},"example":"low"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Voltage divider: low-side thermistor R = Rs·Vout/(Vs−Vout); high-side R = Rs·(Vs−Vout)/Vout. Feed the resistance into /v1/beta or /v1/steinhart-hart to get the temperature.","inputs":{"side":"low","output_voltage":1.5,"supply_voltage":3.3,"series_resistor_ohm":10000},"thermistor_resistance_ohm":8333.3333},"meta":{"timestamp":"2026-06-05T11:30:38.727Z","request_id":"621c1287-2673-4bd1-9737-c5b9d68dcf93"},"status":"ok","message":"Voltage divider","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/steinhart-hart":{"get":{"operationId":"get_v1_steinhart_hart","tags":["Thermistor"],"summary":"Steinhart-Hart","description":"","parameters":[{"name":"a","in":"query","required":true,"description":"Coefficient A","schema":{"type":"string"},"example":"0.001009249522"},{"name":"b","in":"query","required":true,"description":"Coefficient B","schema":{"type":"string"},"example":"0.0002378405444"},{"name":"c","in":"query","required":true,"description":"Coefficient C","schema":{"type":"string"},"example":"0.0000002019202697"},{"name":"resistance","in":"query","required":false,"description":"Resistance (Ω) for R→T","schema":{"type":"string"},"example":"10000"},{"name":"temperature","in":"query","required":false,"description":"Or temperature (°C) for T→R","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Steinhart-Hart: 1/T = A + B·ln R + C·(ln R)³. The most accurate NTC model; coefficients are fitted from three calibration points.","inputs":{"a":0.001009249522,"b":0.0002378405444,"c":2.019202697e-7,"resistance_ohm":10000},"temperature_c":24.6813,"temperature_k":297.8313},"meta":{"timestamp":"2026-06-05T11:30:38.830Z","request_id":"aab3284f-ba9e-41e5-b6b8-c0d34851ddc9"},"status":"ok","message":"Steinhart-Hart","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/meta":{"get":{"operationId":"get_v1_meta","tags":["Meta"],"summary":"Spec","description":"","parameters":[],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"notes":"Resistance in Ω, temperature in °C (kelvin also returned), voltages in V, beta in K. 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