SN 8-bit MCU SN8P2743 Application Practice (5)

Comparator + amplifier connected to SN8P2743 Preliminary test

Based on yesterday's test of 2743 comparator, considering the practical application, it was decided to test it according to the standard double integral measurement method..

To do double integral, you need to use an integrator. Coincidentally, 2743 itself has a very good amplifier, so first use the amplifier to achieve an integrator, and then use a TL431 to generate a precision regulated standard voltage, and divide it to 0.5V through a resistor as the reverse integral voltage. The forward integral voltage is divided to 0.25V.

Since the double integral measurement requires the use of switches to switch the input of the forward integral, signal, reverse integral and other different input voltages, a 74HC4052 is added to the in-phase input of the amplifier. It is a 2*4-way analog switch. Here, only 4 of them are used to switch to 1!

Using the internal oscillator of 243, the code option is 16/4MHZ, and each instruction takes about 0.25uS.

Using timer T0 , select pre-scaling as #70H=0.5uS. Select forward integration time = 7000H, select signal voltage 0～100mV, and take every 10mV as an input test point. Then, run and record one by one to get the following specific data:

 

This data is very practical. Its linearity, resolution and measurement rate are very good, fully meeting practical requirements!

In the table, the adjacent 2 grids are 10mV readings, generally around 114-115 words/mV, and relatively uniform, with almost no nonlinearity! According to this number, the maximum resolution of each word is 8.7uV, and it is completely possible to normalize it to 10uV/word. At this time, it is an order of magnitude higher than the resolution of ICL7107! Equivalent to the resolution of ICL7129!

Moreover, the time taken for each conversion is roughly #7000H*0.5uS=14.336mS, and the reserved margin value is taken = 15mS, which is equivalent to 66.6 conversions per minute.

It is no exaggeration to say that: a SN8P2743 + a 74HC4052 + a 24C02 can be combined into a very good set of cheap and high-quality instrumentation circuits, Its application prospects are very broad!

For the working principle of double integration, please refer to relevant books. ----- This is the application core of many integrated AD circuits, such as: ICL7106, ICL7107, ICL7135, ICL7129 (multiple integration) ..... All of them have this structure. It is insensitive to small-range changes in power supply, and has a strong suppression ability for 50/60HZ power grid frequency and external noise (the working cycle can be arranged to be close to the interference frequency!), which is why the chip's built-in 12-bit AD is discarded! (Because it is too bad!)-------For reference only! [page]

SN8P2743 comparator + amplifier test schematic diagram

Regarding the SN8P2743 comparator + amplifier test, 3 posts have been published before. Due to time constraints at the time, the schematic diagram was not attached, so the schematic diagram is supplemented here.

 
Figure 1: Schematic diagram of an amplifier and three comparators inside 2743, which clearly shows the relationship between the amplifier, comparator and the specific pins of the chip: 

Tip: Some pins of the comparator can not occupy the actual external pins, by using the internal reference and the corresponding status flag to obtain information equivalent to the hardware pin. Therefore, there are 2 comparators that only need to use one port to form a circuit application. It is really the minimum hardware structure!

 
Figure 2: This is the test principle diagram of my uV-level voltage measurement. By adding an external analog multi-way switch, the famous double-integral measurement is formed. The resolution can be as high as < 10uV/word, which is a very cheap and high-quality application.