DS1904L Real-Time Clock iButton
A hardware clock on a key — a 32-bit seconds counter read over 1-Wire.
Adds an accurate real-time clock to any microcontroller over a single 1-Wire contact. Time is kept as a 32-bit binary count of seconds — one-second resolution, over 136 years before rollover — so the same token can time-and-date-stamp events, act as an hour-meter, or drive a logbook. It uses the same binary time format as the DS1994 but is purely a clock, with no interval timer or counters.
A clock, not a memory
Everything else in this category stores data; the DS1904L stores time. It is a pure real-time clock — a 32-bit binary seconds counter driven by a 32.768 kHz crystal, accurate to better than ±2 minutes a month, with 136 years before it rolls over. Touch it to a microcontroller that has no RTC of its own and that device instantly gains an accurate, battery-backed timebase over a single wire. If you want the clock *and* memory in one token, that is the DS1994; if you only need the timestamp source, this is the smaller, simpler answer.
Key features
- A real-time clock in a rugged iButton — adds accurate timekeeping to any microcontroller over one 1-Wire pin.
- 32-bit binary seconds counter: one-second resolution, over 136 years before rollover.
- Clock accuracy better than ±2 minutes per month at +25 °C; oscillator can be stopped in software.
- Family code 24h; unique 64-bit ROM; over 10 years battery life; shares its die with the DS2415 chip.
- Use it for time-and-date stamping, hour-meters, run-time metering and access-time logging.
Specifications
| Chip / compatibility | DS1904 · family code 24h · chip-form DS2415 |
|---|---|
| Memory | 32-bit binary seconds counter (1 s resolution, 136-year span) + 4 user flag bits |
| Protocol | 1-Wire, 16.3 kbit/s; RTC accuracy better than ±2 min/month at +25 °C |
| Package | F5 can |
| Operating temperature | −40 °C … +85 °C |
Inside the stainless can
A 0.25 mm solid stainless shell, a UV-stable polypropylene grommet isolating lid from base, and the die bonded inside. Lid = data contact, base = ground return.
Which memory iButton do you need?
The whole memory range side by side, grouped by storage technology — capacities and family codes per the Analog Devices datasheets.
| Model | Family code | Capacity | Memory technology | Pick it for |
|---|---|---|---|---|
| DS1971 | 14h | 256 bit + 64-bit OTP | EEPROM — battery-free | Asset tag: a locked ID beside rewritable data |
| DS1972 | 2Dh | 1 Kbit (128 B) | EEPROM — battery-free | Per-page write-protect or EPROM-emulation modes |
| DS1973 | 23h | 4 Kbit (512 B) | EEPROM — battery-free | Largest battery-free memory; production travellers |
| DS1982 | 09h | 1 Kbit (128 B) | EPROM — add-only, cannot be erased | Tamper-evident checkpoints and certificates |
| DS1985 | 0Bh | 16 Kbit (2 KB) | EPROM — add-only, cannot be erased | Full append-only service history |
| DS1992 / DS1993 | 08h / 06h | 1 Kbit / 4 Kbit | NV RAM — battery-backed, unlimited writes | Data that changes constantly on the key |
| DS1996 | 0Ch | 64 Kbit (8 KB) | NV RAM — battery-backed, unlimited writes | Portable database — the largest capacity here |
| DS1994 | 04h | 4 Kbit + RTC | NV RAM + clock, timer, counter, alarms | Time- or usage-limited access that expires by itself |
| DS1904L | 24h | No user memory | Real-time clock only | Give a microcontroller an accurate timebase |
| DS1991 | 02h | 1152 bit = 3 × 384 bit | Secure NV RAM — three password zones | Legacy multi-tenant systems (not for new secure designs) |
| DS1961S | 33h | 1 Kbit + 64-bit secret | EEPROM + SHA-1 challenge–response | The anti-cloning choice — proves it knows a secret |
Ordering information
| MOQ | 100 pcs |
|---|---|
| Lead time | 3–7 days for stock items, 10–15 days for OEM |
| Packing | Bulk ESD bags (100–200 pcs/bag, 2 bags/carton); blister or header cards for retail on request |
| Samples | Free samples for volume buyers — courier at cost |
| Payment | T/T bank transfer; other terms negotiable for repeat orders |
| Shipping | DHL / FedEx / UPS air express; sea or rail freight for pallet volumes |
| Customization | ROM ranges · housing colours · laser logo · private label |
Typical applications
Related products
DS1991 MultiKey iButton
Three password-protected 384-bit subkeys in one button.
DS1992 / DS1993 Memory iButton
1 Kb and 4 Kb NV RAM tokens for carrying data on the key.
DS1996 64 Kb Memory iButton
The large-memory token — 64 Kb of rewritable NV RAM.
DS1961S SHA-1 Authentication iButton
1 Kb EEPROM with on-chip SHA-1 challenge–response.