12bitDACの非直線性誤差を自動補正

# dac_sweep.py -- DAC校正自動計測
# DAC基板: COM7 (CDC), コマンド "Dnnnnn\n" (0-10000), 正常時は同一文字列をエコーバック
# DMM   : 34401A, COM9 (RS-232, 9600 7E2, DTR/DSR)
# 出力  : sweep_YYYYMMDD_HHMMSS.csv (input, mV) を1点ごとに逐次書き込み

import serial
import time
import csv
from datetime import datetime

STEP       = 10      # 刻み
SETTLE_SEC = 0.3     # DAC設定後の待ち時間
NPLC       = 10      # DMM積分時間 (10PLC ≈ 200ms, ノイズ除去重視)

# ---- ポートオープン ----
dac = serial.Serial('COM7', 115200, timeout=0.5)          # CDCなのでボーレートは形式上
dmm = serial.Serial('COM9', 9600,
                    bytesize=serial.SEVENBITS,
                    parity=serial.PARITY_EVEN,
                    stopbits=serial.STOPBITS_TWO,
                    timeout=5, dsrdtr=True)

def dmm_cmd(s):
    dmm.write((s + '\n').encode('ascii'))

def dmm_query(s):
    dmm_cmd(s)
    return dmm.readline().decode('ascii', errors='replace').strip()

last_m = None

def dac_set(val, tries=6, wait=1.0):
    global last_m
    tx = f'D{val}'
    for attempt in range(1, tries + 1):
        dac.write((tx + '\n').encode('ascii'))
        t0 = time.time()
        while time.time() - t0 < wait:
            line = dac.readline().decode('ascii', errors='replace').strip()
            if not line:
                continue
            toks = line.split()
            if toks[0] == tx:
                dt = time.time() - t0
                m = next((int(t[1:]) for t in toks if t.startswith('M')), None)
                if dt > 1.0 or attempt > 1:
                    gap = (m - last_m) if (m and last_m) else None
                    print(f'  * {tx}: 受信{dt:.1f}s (試行{attempt}) M={m} M間隔={gap}ms')
                if m: last_m = m
                return
            print(f'  * 読み飛ばし: {line!r} (待機中: {tx})')
        print(f'  * {tx}: 応答なし、再送 ({attempt}/{tries})')
    raise RuntimeError(f'エコー待ちタイムアウト: {tx}')

fname = datetime.now().strftime('sweep_%Y%m%d_%H%M%S.csv')

try:
    # ---- DMM初期設定(1回だけ) ----
    dmm_cmd('SYST:REM')
    time.sleep(0.3)
    dmm_cmd('*CLS')
    dmm_cmd('CONF:VOLT:DC 1')            # 1Vレンジ固定(オートレンジ切替遅延を排除)
    dmm_cmd(f'VOLT:DC:NPLC {NPLC}')
    dmm_cmd('TRIG:SOUR IMM')
    err = dmm_query('SYST:ERR?')
    print('DMM設定完了, ERR:', err)

    t0 = time.time()
    with open(fname, 'w', newline='') as f:
        w = csv.writer(f)
        w.writerow(['input', 'mV'])

        points = range(0, 10001, STEP)
        for i, val in enumerate(points):
            dac_set(val)
            time.sleep(SETTLE_SEC)
            resp = dmm_query('READ?')
            mv = float(resp) * 1000.0
            w.writerow([val, f'{mv:.4f}'])
            f.flush()                    # 中断しても途中まで残す

            if val % 500 == 0:
                elapsed = time.time() - t0
                total = elapsed / (i + 1) * len(points)
                print(f'{val:5d} : {mv:9.4f} mV   '
                      f'[{elapsed/60:4.1f}/{total/60:4.1f} min]')

    print(f'\n完了: {fname} ({len(points)}点, {(time.time()-t0)/60:.1f}分)')

except KeyboardInterrupt:
    print(f'\n中断: 途中までのデータは {fname} に保存済み')

finally:
    try:
        dac_set(0)                       # DAC出力を0に戻す
    except Exception:
        pass
    dmm_cmd('SYST:LOC')                  # DMMをローカルに戻す(フリー測定再開)
    dac.close()
    dmm.close()

#define DAC_CAL_N     1001
#define DAC_CAL_STEP  10

// 実測出力 [mV] : 入力 0,10,20,...,10000 に対応 (約4KB)
static const float dacMeas[DAC_CAL_N] = {
       0.8987f,    0.8988f,    1.4495f,    2.4815f,    3.5046f,
       4.9004f,    5.8884f,    6.9116f,    8.3171f,    9.3706f,
     中略　・・・・
     987.8415f,  988.4052f,  989.1784f,  989.7413f,  990.3195f,
     991.0516f,  991.5987f,  992.1509f,  992.8999f,  993.4584f,
     994.0397f,  995.4857f,  996.7149f,  997.9571f,  999.6010f,
    1000.8718f
};

void da_set(int16_t val) {
    if (val < 0)     val = 0;
    if (val > 10000) val = 10000;

    float target = val * 0.1f;   // 目標出力 [mV]
    float x;                     // 補正後の等価入力値 (0-10000, float)

    if (target <= dacMeas[0]) {
        x = 0.0f;
    } else if (target >= dacMeas[DAC_CAL_N - 1]) {
        x = 10000.0f;
    } else {
        int lo = 0, hi = DAC_CAL_N - 1;
        while (hi - lo > 1) {
            int mid = (lo + hi) >> 1;
            if (dacMeas[mid] <= target) lo = mid;
            else                        hi = mid;
        }
        float y0 = dacMeas[lo];
        float y1 = dacMeas[lo + 1];
        x = (float)DAC_CAL_STEP * ((float)lo + (target - y0) / (y1 - y0));
    }

    float fval = x * 0.3344f;
    I2Cdevice.i2c_mcp4726_write(I2C_MAIN_NUM, (int16_t)(fval - 0.5f));
}