DuraNAV – Hardware Manual
18
Electrical Specification for input signal:
Voltage range: 0 ~ 36V
High / Low threshold: 2 ~ 20V software selectable
Maximum input frequency: 10kHz
Minimum High Time: 40us
Minimum Low Time: 40us
Odometer Supply:
A voltage output for an Odometer device is available on pin "ODOMETER_SUPPLY".
Note that common GND pins are used as reference for "ODOMETER_SUPPLY".
The voltage supply is jumper selectable between 5V and the "VIN+" (battery) voltage.
In both cases, the output current is protected over the threshold of 200mA.
Refer to The Jumpers and their functions paragraph for further information about the jumper selection.
Selection of threshold:
The odometer circuit compares the input signal with a software programmable threshold, and uses the
comparator output as the clock of a 16-bit counter.
The purpose of the programmable threshold is not to measure the value of the input voltage, but to allow the
system integrator to choose the best threshold value for his application.
First, the odometer input signal is applied to a resistor divider with a ratio of 1:4.7, with 100kOhm input
resistor. Then the signal is compared with a programmable reference voltage from 0 to 5V in 64 steps of
78mV each.
The programmable reference voltage comes from an EEPOT device, whose wiper position is programmed at
power-on and stored until next power-down or reprogramming.
Note that due to tolerances and rail limits, the lower and upper limits of reference voltage are not usable.
There are 55 usable threshold values, which correspond to wiper position from 6 to 60.
The comparator itself has 15mV of hysteresis for a clean transition.
On the following table, there are the allowed wiper position and the corresponding threshold, with a 4%
tolerance.
Wiper
step
Threshold Wiper
step
Threshold Wiper
step
Threshold Wiper
step
Threshold
1 Unused 17 6,41 33 11,98 49 17,10
2 Unused 18 6,78 34 12,32 50 17,41
3 Unused 19 7,14 35 12,65 51 17,71
4 Unused 20 7,49 36 12,98 52 18,01
5 Unused 21 7,85 37 13,31 53 18,31
6 2,32 22 8,20 38 13,63 54 18,61
7 2,70 23 8,56 39 13,96 55 18,91
8 3,08 24 8,91 40 14,28 56 19,20
9 3,46 25 9,26 41 14,60 57 19,49
10 3,84 26 9,60 42 14,92 58 19,78
11 4,21 27 9,95 43 15,24 59 20,07
12 4,58 28 10,29 44 15,55 60 20,36
13 4,95 29 10,63 45 15,87 61 Unused
14 5,32 30 10,97 46 16,18 62 Unused
15 5,69 31 11,31 47 16,49 63 Unused
16 6,05 32 11,65 48 16,80 64 Unused