140 lines
4.6 KiB
Markdown
140 lines
4.6 KiB
Markdown
# HP3478A Internal USB-GPIB Extension
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An internal extension board for the HP3478A Multimeter. USB-CDC-GPIB bridge (Prologix-style) and an internal feature controller.
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Uses WCH CH32V203 (RISC-V) MCU.
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It enumerates as a standard serial device (e.g., /dev/ttyACM0 or COMx).
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PCB [here](https://git.ayau.me/mira/mhardware/src/branch/master/hp3478a-ch32-ext)
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More photos in [img/](./img/)
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## Menu System
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Extended features (Continuity, Temp, etc.) can be accessed using the SRQ button of HP3478A without a PC
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1. **Enter Menu:** Press the Front Panel **SRQ**.
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2. **Nav:** Press the button again to cycle through modes (`M: REL` -> `M: TEMP` -> `M: DBM`...).
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3. **Selection (Hover):** Stop pressing the button.
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- The display will animate dots (`...`) after 500ms.
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- After ~2.5 seconds of inactivity, the selected mode is activated.
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4. **Sub-Menus:** Some modes (like Temp) have sub-menus for sensor type and 2W/4W mode. Same cycle logic to select these.
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5. **Exit:** Press the SRQ button to exit back to initial mode (one we entered menu from).
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## Features
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These can be triggered via the Menu or the serial commands below.
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Relative and Statistics depend on the mode you enter the menu from, i.e. if you enter relative from DCV it saves your state and you get relative voltage, from 2W relative 2W etc.
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```
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++help
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HP3478A Internal USB-GPIB 1.2.0
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[GPIB Setup]
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++addr <0-30> Target Address
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++auto <0-2> 0:Off, 1:Read-After-Write, 2:Query-Only
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++read_tmo_ms <t> Timeout in ms
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++eoi <0|1> Assert hardware EOI on write end
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++eos <0-3> Write Term: 0:CRLF, 1:CR, 2:LF, 3:None
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++eor <0-7> Read Stop: 0:CRLF ... 7:EOI-Only
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++eot_enable <B> Append extra char to read output
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++eot_char <dec> The char to append
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++dmm_loop <0|1> Toggle HP3478A loop, if it conflicts w/ GPIB bus
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[System Configuration]
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++config List all configurable parameters
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++get <name> Get parameter value
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++set <name> <v> Set parameter value
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++savecfg Save config to flash
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++ver Firmware Version
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++rst System Reset
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[GPIB Bus Operations]
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++read Read from target
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++write <data> Write to target
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++trg Device Trigger (GET)
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++clr Device Clear (SDC)
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++dcl Universal Device Clear (DCL)
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++ifc Interface Clear (Bus Reset)
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++spoll [addr] Serial Poll
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++srq Query SRQ Line (0=High/Idle, 1=Low/Active)
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++loc Local (Drop REN)
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++llo Local Lockout
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[Internal HP3478A Features]
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++cont, ++hold, ++rel, ++xohm
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++dbm, ++diode, ++math, ++norm
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++temp <l1> <l2> Temperature sensor mode
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++env [temp|hum] Internal AHT20 Sensor
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++disp <text> Write text to LCD
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```
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There's also a configuration which can be saved using `++savecfg` if you want to make it persist (it's saved to v203's "undocumented" flash).
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Also see [inc/config.h](./inc/config.h).
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```
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++config
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my_addr: 0
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dmm_addr: 18
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target_addr: 18
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eot_char: 0
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eot_enable: 0
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eoi_assert: 1
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eos_mode: 0
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eor_mode: 0
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auto_read: 0
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gpib_timeout_ms: 1200
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poll_interval_ms: 100
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env_sensor_read_interval_ms: 1000
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dmm_recovery_delay_ms: 1000
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usb_debounce_connect_ms: 50
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usb_debounce_disconnect_ms: 200
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usb_timeout_target_ms: 5
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menu_dot_interval_ms: 500
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menu_commit_delay_ms: 2400
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menu_sublayer_delay_ms: 500
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menu_debounce_ms: 100
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menu_lockout_ms: 1000
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stats_cycle_time_ms: 3000
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cont_disp_update_ms: 150
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diode_stable_ms: 20
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buzzer_chirp_hz: 3000
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buzzer_chirp_ms: 75
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buzzer_cont_hz: 2500
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rtd_a: 0.003908
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rtd_b: -0.000001
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rtd_r0: 1000.000000
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cjc_fallback_temp: 22.000000
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cjc_self_heating_offset: 4.000000
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type_k_scale: 24390.240000
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dbm_ref_z: 50.000000
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diode_th_short: 0.050000
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diode_th_open: 2.500000
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autohold_threshold: 1.000000
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autohold_change_req: 2.000000
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autohold_min_val: 0.050000
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cont_threshold_ohms: 10.000000
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autohold_stable_count: 3
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rel_stable_count: 3
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```
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i.e.
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```
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++set dbm_ref_z 60
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++savecfg
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```
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Now your dBm feature will use 600 ohm ref instead of 50.
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## Known Issues
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1. I did NOT use the brain when routing the USBLC6. Either have to DNP the IC and jumper the data lines, or rely on the software hack to check USB `SUSPEND` to guess if the host is connected. I do the latter, works but meh. VBUS detection would be nicer.
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2. The buzzer is **not on a hardware TIM pin**. It's on a generic GPIO... This means it can't be hardware/timer PWMed. Instead, the firmware is firing a TIM IRQ thousands of times a second just to manually toggle the pin in the ISR..
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3. There is a microSD card footprint on the board. The fw does absolutely nothing with it. Data logging?
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