For the application code main. The first thing to note, that this system is an interrupt-driven one. Which means the main super loop is empty. Main tasks are handled in the ISR routine as you can see in the attached code.
The other thing to note is that this system keeps switching from one state to another. Then take the measurement convert it to an analog voltage by updating the PWM duty cycle and also send out a UART string with the measured value.
We can now start making our first prototype on a breadboard just to test the hardware and firmware parts of this project. Here is a short demo video for the running test on the breadboard. Just to validate everything before moving on to designing a PCB for the project hardware.
To avoid having to go through a rework revision of the board in the future. By testing a 10kHz input signal, the output will be 2. And our board output voltage will be linear sweep from 0v up to 5v back and forth.
This is a linearity check over the entire input range just to validate the system at all possible input frequencies.
The output will be a linear triangular wave on the DSO. The first step in the PCB design is to finalize the schematic design of the board and then do the schematic capture to the CAD software tool. And here is a screenshot of the finalized schematic design for the board. Generating Fab. The final step is to generate the fabrication-ready output files Gerber to be sent later for manufacturing.
Also, the curve is delayed by a few tenths of a second between the true Hz and the voltage curve. Is this typical? I am attaching a snapshot of a spreadsheet that I made so you can see the delay that I'm talking about, but the data is only sampled every 0. Also, I scaled the output voltage by 50 to show that it compares to the Hz input.
I am not sure what you mean by a "grinder" except for possibly a grinding wheel used in machine shops? I do expect the LMN perfomance to be predictable and repeatable.
If there is variation in the input signal the voltage in relation to time, the LMN output voltage will track with it. Noise riding on the input signal can lead to this uncertainty. You don't mention what sort of assembly the LMN is part of, but make sure that it is properly housed in shielded enclosure if there is the possibility of noise getting into the comparator inputs.
The shielding should be extended to any input line, coax or twisted pair, from a transducer. Be sure the supply voltage applied to the LMN is well regulated and free of noise. One of the reasons for the LMN version of the product and the inclusion of the internal zener regulation is to assure a more constant Vcc level in loosely regulated appications. The datasheet doesn't mention anything about the time required to accomplish the tachometer-to-voltage conversion, but it stands to reason that the charge pump circuit requires time to charge and discharge when converting the input pulses to a dc level.
Certainly, if you are observing delay it is a normal characteristic of the conversion process. Just wondering what could cause this? Also, the orange line is the frequency and you can see that right after the peak frequency, the ratio jumps up quite a bit - almost like its experiencing some sort of hysteresis.
Using a scope, I watched the input frequency. It stays high at 11 V and dropped to 0 once per revolution. Does the converter expect this signal to be inverted, staying at 0 and jumping to 11 V once per rev?
I'm also exploring the option of using Figure 27 from the data sheet. It claims that it reduces ripple which seems to be exactly what I need. This is true even without triggering, which of course occurs only upon the next subsequent rpm pulse. The advantage is that a drop in rpm is recognized rapidly. This pulse former circuit substantially comprises a differential amplifier 45, the negative input of which is connected via a series circuit of two resistors 46 and 47 with a first connection point of a two-stage voltage divider comprising the resistors 48, 49 and 50 between the positive line and the negative line; its positive input is connected via a resistor 51 to the second connection point of the voltage divider 48, 49, The input signals are present at an input terminal 53; they are limited in their amplitude by means of two diodes 54 and 55 switched in parallel to one another and are fed via a capacitor 56 to the junction point of the two resistors 47 and Finally, there is also a positive feedback circuit, comprising a feedback capacitor 57 at the differential amplifier 45 and a resistor 58, from the positive input of the amplifier 45 to the ground line On the output side, the amplifier 45 is coupled with an output terminal 60, which may be connected directly with the input terminal 10 of the circuit layout of FIG.
The signals from any arbitrary rpm transducer reach the input terminal 53 and from there pass via the capacitor 56 to the negative input of the amplifier The negative half-wave of the transducer signal switches over the amplifier 45, which is functioning as a comparator; this triggers a time function via the capacitor feedback, so that positive pulses of a predetermined minimum duration appear at the output of the amplifier These pulses, given an appropriate dimensioning of the timing element, are embodied such that they suffice for the complete reloading of the input capacitor 11 of the circuit layout of FIG.
The above-described circuit layouts, despite their relatively simple structure, are distinguished by their surprisingly precise functioning, which suits them above all for high-quantity mass production. In terms of their technical exploitation, it has proved to be particularly advantageous that when the rpm drops, there is no need to wait for the next subsequent trigger pulse; instead, the output voltage already changes as soon as the period duration corresponding to the old rpm is exceeded.
The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other embodiments and variants thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims. What is claimed and desired to be secured by Letters Patent of the United States is: 1. An rpm-to-voltage converter for controlling an internal combustion engine having an rpm pulse generating means which comprises: a direct voltage source;.
DE DEA1 en USA en. JPSA en. Here is the circuit I have done:. The resistor, capacitor and the diode connected to the tach signal wire is to get rid of the DC offset.
There are 2 problems at the moment:- 1 The chip doesn't convert the signal properly, the higher the RPM from the car the less accurate the output voltage, hence a very off RPM compared with the RPM dial in the car. A quick look at the datasheet suggests the diode on the input isn't necessary, it seems desined to have the tach ac input, no experience with the ic tho. I've checked the current that the circuit takes and it's about 65mA.
It's supposed to take less than 5mA. This is with the input signal frequency and the output voltage disconnected. That schematic indicates they shouldn't be, but with that style it would be easy to misread that. Yep, that was why I asked. I suspect the OP might have wired those connections by misreading the schematic. What happens is that the diode is cut off by the dc generated from the input pulses.
Another thing I've found is that the reason why at higher RPMs it lows lower, is that, since the chip was getting hot the accuracy was dropping, so it seemed it was reading incorrectly.
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