Jump to content
Electronics-Lab.com Community


  • Posts

  • Joined

  • Last visited


Everything posted by Tony_Stoynov

  1. Hi to all, yes, for my practice i see a several stranges in 78xx behavior. 1. This i think all must know, must have a good frequncy capacitor, ceramic 47 or 100 nF is good, this capacitor must be in input and utput, to prewent oscilation process. 2. The temperatute problem, in NS or ST documentation can see that the operating range is up to 150 C. I can sugest to calculate the working condition up to the maximum, but i have the problem at a considerable low temperature, no more that 80 C. I not say that i see this promblem with NS or ST chip, but i bay chip from distributor, put in the bord and start the device. The result is that after several minutes,i see the problem with a LCD. The first thing in a minde is for a software problems, becouse the RS comunication work correctly, and the LED indicator work. I check all soft, and finally i open the device case to change the display .. may be .. no matter how i finde the problem, but finally the problem was unstable voltage. When i connect the scope, and close the device box, after several minutes i see pulsations, may be around 1 - 0.5 Hz. I mesure the 78xx temperature with closed box, and if i remember right, the temperature was around 80 C. I solve this problem with a small heatsink, but on other device i have similar power over 78xx, but i not see this problem. The my conclusion is that some chips, not wrk very good on hight temperature. 3. Input voltage, agin acording to NS or ST documentatin, the max input voltage for 7805 is 35 V, for 20,24 series in t documentation the max input voltage is 40 V. But ... this is deend from the manufacture for example, in some east europian parts, this voltage is a 12 V. I find that this is not only in some of east europian part, like a Bulgarian version or MA7805 version /i think this part not in the production now/ but in some other chips, i not write the number, but i buy this device from big distributor. 4. The noise attenuation. If have a some interference on the power line, and if this is a high frequency interference, speccially pulse interference, is a very possible this interference going directly to the output, whit a very low attenuation. The one of the big problem that i see in this aspect, was wit a device that controled 220 V realy, and the efect is that eery time when i switch off the relay, the pic going to reset. When i put the scope to power line, i see a strong impusl, that restat may processor, no matter that i have a 1 k from reset to Vcc and i am use the internal reset ciruit. I tray to use the LC filter, but the effect is to same, i solve the prblem in prototype with LC filter befor 220 V transformer, but i the serial production dvice i change 7805 with a 2575-5.0, in standart schem, without any extra filters. Ok this is some of stranges in behavior. For the first one, you can see info in application note,this is easy to be solved. Second, and third problem, i know that this is depen from the manufacture, now i buy only this device that i have documentation for, and that hve a good quality. The last stranges, actually ths is not a stranges, this is a chip parameter, but many people look at data sheet, and the see that ST give around 60 dB attenuation for 100 k, or NS give 45 dB at to same frequency, but this is attenuation for sin signal,not for impuls with a steep front.
  2. Hi, what is the supply of your trigger, and way if you have a uC put this shmid trigger. If the output of your triger not going to 12 V you cn have a problem, actually you wil have a problem, becose your PNP will be open. To control the transistor is used the current Base-Emiter. In your case, if you have 5 V on the base, and 12 V on the emiter, you will have a emiter to base current that will open the transistor. This curent is limited from trigger high level current and your base rezistor. In your case the output will be always high, and the mosfet wil be always ON. You can use the NPN tranzistor.
  3. Hi, this is depend from the technology, in some chips have a curent sources, on some chips the limit is from high side structures. Not in every chips have a different between two curents. RTL is a rezistor transistor logic, in this type of logic is a normal to have a much higer current t grond, becouse the high level is provide from pull up rezistors. In the new TTL or CMOS, output is PNP-NPN or P-N chanel transistors, but actually this is like more easy that is in reality to obtin the high frequency have a many diferents way to improove the circuit, but some of the limitation is this differents, but how i say before, this is depend from the chip.
  4. Hi, to Ante, one remark, yes the FPGA is not a CPU, but .. i think is not very far from MCU. The princip is different, but in this moment in many FPGA application is used IP core for different procesor, and second, for FPGA is used program languages. About this when you can use FPGA and when MCU. The question is very difficult, the FPGA or CPLD is a logic elemnt, and you can create many differents configuration between. The one of the best way is to combine logic and MCU, but in different case you can use mcu or fpga, actualy this is valid for complex procces. For example, if you want to have a SDRAM or DDR interface, but your CPU nt have this interface, the only ine way is using the CPLD or FPGA. If you have a need off fast respons and fast signal dating, i talk for a digital signal the logic is better, one of the advantage is the high frequency, and paralel processing. For exampel, if you have several different signal, and whant to make some datting, let this is sum betwen sygnal, for examlple A,B,C 4 bit bus, in FPGA or CPLD the output response is depend only from CPLA element delay, in this case around 10 ns, for CPLD, in to same case in microcontroler you must read different signal, after then make a sum, but this is not a parlel proces, you first read, A, after this read B, after this C, after this add A to B, after this add B to C, and finally put the result in to output, how you see this is many opperation, and if yu use the RISC cpu, at 20 Mhz, and 1 instruction for clock = 50 ns, the response time will be no less that 300 ns, if the cpu architecture can solve the problem with 6 operation. The advantage of FPGA is that you can put CPU core in to chip, and combine it with other logic. Very good example is the car ECU, for good engine control, you must can control evry chanel searetly, if you have 6 cylinder engine, this is a 6 chanel for ignition, and 6 chanel for injection. Ok, good resolution is 1 uS, then you must have a 12 indipendent chanel, that can caontrol delay after some sync signal, and send impuls with some weidth. If you use CPU, this is not very easy, becouse you must look at 12 different timer, or counters, and compare it value to some variable. The CPU can do this, if CPU have several capture - compare modules, and you set some limitation on the sygnal condition, then you can make this. If you use logic, this is a very easy to be solved, you must put several counter and comparator, and this is all, you can use any resolution up to 10 ns, and you will have a 10 ns response time. On the other hand, for this ECU you must calculate several parameters, delay and impuls weidth, if you use the FPGA for this, you must use IP core, but for this you must have a bigger FPGA, on the other hand every CPU canmake this calculation very easy, because this is not a very fast procces. And ... the result you have several way, to use cpu with many CCP modules, but this is not guaranty that all wil be OK, to use the big FPGA with IP core, this is a very good solution, may be more costly, or to use cpu and CPLD combination. Another example is digital analisator, in this case you can't use the cpu, becouse you have a need off very fast response. But if you want to make some simple protocol converter, may be is better to use the CPU. I can give you many different examples, but better is to understood what is the differents, and what is the advantage of the CPU and logic, FPGA or CPLD. p.s. may be this is not very good english, and can't get the pulicer but i hope you will understood me.
  5. Hi, i don't think that you have need from project, the transistors is not simple device, you can understood how exactly work from one project. I will upload the file that can help ypu to understood how work the transistor. This is first part, for bipoliar transistors, sory for bad qualiy, but i think this is a very usefull book. [attachment deleted by admin]
  6. Hi, yes in the internet has a many circuite diagram, you can look at www.national.com ot wwwintersil.com, and also www.analog.com, in this website you can see different aplication notes. You must have a minde that phototransistor is more sensitive, compared with a photodiode, and is a very easy to saturate it. Base yuo can leave not connected, but with the base you can compensate some problem with saturation, and with a noise.
  7. Hi, you can use the SMPS, some like the LM2575, but with a current feadback. Another choicesh is t use linear regulator, LM317 etc., but in this case the power over the regulator will be higer, for example, if you use 2575, and for 500 mA he voltage over the photodiode is around 3 V, and your power supplay is a 12 V, then over the LM2575 you will have around 0.5 W, in too same case over the LM317 you will have a 4.5 W, this is a big different. If you have a uC you can use the integrated PWM module and ADC or compartor to realize the current source.
  8. Hi, You can use just one bateries, a 9 V cells, or a 3 LiOn cells, this will give you around 11 V, depent from the current that you will be need have a different possibilities, if can give me us more specific parameters, specially current, we can give you the best decision. p.s. why you use 9 V, why not use a 3 or 5 V schem?
  9. Hi, in the post above, you can see ones of the possible decision, but this decision has one disadvantage, minimum dispersed power @50 mA is it around 5 W. If you not have a space for a big components, or you want cold device, the better choices is using of SMPS, i can suggest TNY series from Power Int. Look here : http://www.mcu-bg.com/mcu_site/viewtopic.php?t=1052&postdays=0&postorder=asc&start=75, you can see the TNY and TOP sch, also if you look at all topic, you can see the different diagram for directly 220 V power supply.
  10. Hi, if the output is a digital, PWM or Impulse will be better if you use a microcontroler, PIC10 or PIC12. If the output is analog, you can use simple comparator. One another possibilities is useng a Frequency to Voltage convertor, if the output is a Impulse, and comparator after the convertor,but this will be a less accurately, and wil need min. 2 chips. Whit microcontroler you can do this very ease.
  11. Hi, Yes you can, but must think about input offset voltage, you must make the input compensation. I can suggest to use more precision OPAMP, something like MCP606/7/8/9 from Microchip or OP-41, OP-07 etc.
  12. Hi, dependce form the motor i can suggest yu to use the curent control, in this case the suply voltage for the steper can be 24 ot 48 volts, you will cntrol the current. But if want to test on he low speed may be this is too complex decision. To conol the output voltage you have several possibilities, first use DAC external or change the PIC whit ther uC with integrated DAC. Second use digital potenciometer, and control the output voltage. Third use the PWM for generate the control sygnal for the regulator, or ue directly this PWM to generate the voltage that you need. In all case you must have feedback, for this can use the pic ADC, or if not have a internal ADC, can use a external one.
  13. Hi MP, you are very right, for a uC he will need more experience, a PLC may be will be more easy, but again will need some experience and knowledges that i think he not have. But if using a simple timer and counter modules will need just to make the connection between them and we can give him the shematic diagram. About the process, this is a bending machine for tube, i see this type of machine, and know how it's works. To make a bending with fixed radius is need several time to repeat too same process, because if you try to make small bending radius on one time, in better case you will have bad quality. If you want to make a 50 sm radius for example, first you must made 2 m, after this 1 m, and then 50 sm, to prevent a tube bashing. Actually this is not complex in meaning that is a very difficult, but need to repeat several time one operation. I understood that he want to put the tube, set the need radius or number of cycles and role movement, run the machine, and machine say "I am ready" when finish the operation :)
  14. Hi, I understand that he want to automated all process, the process is complex, first moving role down,bending, moving down, bending .... to the moment when have a required radius of bending. For this reason i think is need something more that switch, but if he use a counter and timer, i think can do this very easy without any program. Have a many different counters and timer, mechanical, electromechanical ot electronics, they is made exactly for this type of needs, in this case user will set a numbers of the cycles, and the time to moving down.
  15. Hi, you have a two possibilities, first is buy a controller, many company have a controllers that work with user software, Siemens, Honeweel, Rockweel etc. this is a PLC controllers. Second way is to make own contorller, but if you want to program time and cycles, you must use microcontroller, but this not be a very easy for beginner, the another problem is that this is the machine, and i think this machine will work in a workshop where have other machines, welding, cutting etc. If this is right, the controller must be with really good soft and hardware, to prevent any EMC problems. This is not very difficult if you have a experience, but if you never do this,not be a very easy for you. Actually have one more way, to using a standard counter and timers, and made the relay circuits.
  16. Hi, if you look at forums above, you wil see may post with C source for the 16F628 controller, i think this is a good solution, 16F84 not have a hardware RS and this may be a problem for you, because you not have a experience in to the uC. The ideais o generate fixed time delay, on 1200 b/ps you have avalible bit every 833 uS. After receiving the start bit, this must be connect to the interrupt input, B.0 for example, you start your time delay, for example, first generate 416, get first bit, after that wait 833 and get second, 833 third ...... but this is not the most good way to make a software RS, all is depend from CPU usage, if your CPU have a time, you can use frequency 10 or 20 time high, and use this frequency to read the data. This will give to you more flexability.
  17. Hi, yes you can use 555 or something other chip, actually 55 may be not a very suitable for this application. I know that exist, but never not use a on chip converter, this is small chip that convert frequency to voltag. Ok i will see for some good analog decision that is not a very expensive. Why you dont want to use a microcontroller ? Will be very easy and simple :) I will try to make this schem for you in the next several days, if have some free time today or tomorrow. Edit You can find the LM2917 chip in your country?
  18. Hi, Yes, the LM393 for example, but you must have a hysteresis.
  19. Hi, you need a frequency meter mode, with 1 Hz time for measuring. See the attached file, only i'm not suare how must set the channel, if may be you can connect to input together, to be sure that every time will measure the signal. And .... im not suare if the chip have a current limit for the LED, if not have internal limitation you must put external resistor on a,b,c.....g wire, around 200 Om. The good idea is to use comparator for the input signal, with hysteresis. counter.pdf
  20. Hi, the ICM7226 is the most simple decisiaon, this or somethin like this chip. The next possibility is to use the uControler, in the web yu can find many diagram with PIC 16F84. But for this you must have programer etc. Another way is to use frquency to voltage converter, and use the standad module wit ICL7106 or some equalent, but this is i thin is not a more simple. You can bay the frefuqncy meter modul and use it. But i can't understand were is the problem ith 7226, the circuit is a very easy to use, you wil need only several external component. No need to use all 8 LED, you can use only 4. To realize this with the standart logic will be more expensive, and will need to use no less that 6 IC if use counter with a LED output, or 13 IC if use standart counter and binary to 7 segment decoder.
  21. Hi, OK, in this case +/- 5% you can use counter mode, because if you want high precision you must measure impulse time, and for this some suitable is uControler, but in your case this is unnecessary. You can use something like a ICM7226. For sensor, in this case using of reflective sensors is a most suitable, because 15 sm is the long distance, and have a big possibility to wrong detection.
  22. Hi, yes LED and phototransistor is ideal for this application, but if this disk is not very wide, you can use optocoupler with air gap, like a this in some PC mouse. If this disk is made from metal, steel or other magnetich material, also you can use the hall sensor. For counting have different ways, use the onchip counter, or use uControler, Pic, AVR etc. But .....i don't know what is the accuracy that you want. For example if you have 4 impulse per turn, and the speed is 3600 rpm this is a 60 turn per second, or 240 impulse per second. The resolution will be 3600/240 or 15 rpm. This is the +/ 0.41 %. But if your speed is low, 360 rpm for exampel this is a 6 turn per second or 24 impulse per seconds, then the resolution is 360/24,again 15 rpm, but this is +/- 4.1 %. p.s. my english too is no very good, i hope that you will understand me
  23. And don't forgot that not all DC motors can be reversed only with change power supply. Depend of the construction: permanent magnetic, parallel or serial stator you must change poliarity of the rotor or stator or both of them.
  24. Hi leowjunwei, i not forgot, but i just change the file in my previews post, but i will atach the file to this post too. RS_PS2.pdf
  25. Hi, If you have a +5 you must use exactly this to make 3.6, no any reason to make 4 and then from 4 make 3.6. In post above this 0.4 V is the differences between input and output, the 0.4 V is a very small difference, many of good DC-DC chips work with different around 0.8 V, but if you have a 5 V then you have not a problem. If the input voltage is 5 and the output is 3.6 this is a 1.4 V over the regulator, this is the 14 W, not very easy to be cooled. My suggestion is use the DC-DC convertor, the LM2743/45/48 or something like this.
  • Create New...