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  1. KrisBlueNZ

    High Power Dual H-Bridge

    H-bridge technology has improved since the L293. Modern devices use MOSFETs with relatively low ON-resistance and high current capability. Unfortunately for you, they're not pin-compatible with the L293. Also many of them are surface-mount packages. So I think your option 2 is probably your best...
  2. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Yes, you can get op-amps that swing rail-to-rail (or very close to), as long as they're not heavily loaded. But as I explained, you don't need it. You just need to buffer the cutoff voltage; the other two voltages (battery voltage and SNK voltage) don't need to be buffered. Actually you can...
  3. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    You mean mV not mA, right? The op-amp output won't swing all the way to the positive supply rail. Especially for the LM358 which is a very old device, but the TLE2022 will not swing all the way either. Your best option is to buffer the cutoff voltage, and switch the meter input between +BATT...
  4. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    OK, I'm glad you've got it working. I won't check your layout drawing... since it's working, there's no need. I would replace the MTP3055 with a 2N7000. The 2N7000's minimum Vgs threshold is 0.8V, not 0.08V. The gate voltage in that circuit should be less than 0.8V. Perhaps there is still an...
  5. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Did he work from my original schematic? OK. You could use a TLE2024, the quad version of the TLE2022. The main reason I chose the TLE202x over the LM324 or other low-quality devices is the low offset voltage. I think your schematic is right. (My diagram is drawn with a very old program called...
  6. KrisBlueNZ

    Transistors as switch

    I don't know what you mean about "U643B". It's not shown on your diagram and I didn't suggest it. You could use a piezo transducer to make the clicking noise. That would be cheaper and smaller than a relay. Your best bet is definitely a microcontroller.
  7. KrisBlueNZ

    Transistors as switch

    There are a number of problems with that design. The diagram will be clearer and easier to follow if you put the 0V rail along the bottom and the positive rail across the top. Also, having the relay shown separately adds a lot of unnecessary confusion and opportunity for error. I would use a...
  8. KrisBlueNZ

    Transistors as switch

    If you Google "op-amp oscillator" you will see lots of image hits for the same standard circuit, which uses one op-amp, three resistors and a capacitor. But like the 555-based oscillator, this circuit is not easy to modify so its frequency is switchable by a signal, especially if the duty cycle...
  9. KrisBlueNZ

    Why is the bias in volts if a BJT is current driven?

    The more voltage you apply on the gate (with respect to the source), the more current can flow through the MOSFET in the source-drain circuit. This assumes that the connections to the source and drain are such that current can flow through into the MOSFET's drain and out of its source (i.e. in...
  10. KrisBlueNZ

    Transistors as switch

    OK. Changing the voltage at pin 5 is not the answer for this application, because it will also greatly affect the duty cycle. But changing the resistance between pin 7 and pins 2,6 is not simple either. In this case I think a 555 is probably not the best option. Can you describe the constraints...
  11. KrisBlueNZ

    Transistors as switch

    I think you want to switch your astable circuit between two different frequencies. Is that right? There are other simpler ways to do this; a common way is by changing the voltage at pin 5. If you explain what you want to achieve, not how you think you need to achieve it, folks here will be able...
  12. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    I just noticed that the optocoupler's collector and emitter are reversed on the schematic. The emitter should be connected to the 0V rail. I assume your prototype has the correct connections; if it doesn't, I can't see how the optocoupler would work at all. I'm not happy with the RM change...
  13. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Hi Greg, I'm glad you have a circuit that you're happy with. I think the optocoupler you added in the power-up/power-down control loop may have fixed the problem not because it provides isolation, but because of its delayed turn-off. If it delays the feedback loop long enough for the supply...
  14. KrisBlueNZ

    Programming of MUC

    OK. I don't want to give you a complete answer because this is obviously a school project. You need to divide this task into several stages. These can be written as separate functions, to keep the organisation of the program clear and easy to understand. This will also impress your tutor...
  15. KrisBlueNZ

    Programming of MUC

    I'm at my partner's house and I don't have fast internet access, so I'm afraid I cannot watch your video until Tuesday. Can ANYONE ELSE help before then? Otherwise, I will reply on Tuesday. BTW, please don't call me sir!
  16. KrisBlueNZ

    Can I return to a return?

    Source code consists of two parts: comments, and code. The comments are solely for people (including the author - actually, mainly the author) to read. The code is for the author to read and for the processor to execute. (And for the compiler to compile, if it's a compiled language.) All three...
  17. KrisBlueNZ

    Can I return to a return?

    These are the notes I made while reading through your program. I haven't identified the bug, but I strongly suggest you follow this advice. When you do, the cause of the problem will _probably_ (based on my previous experience) become obvious to you. Even if it doesn't, improving the quality of...
  18. KrisBlueNZ

    Programming of MUC

    The purpose of keeping last_port_status is to avoid updating the LCD each time through the loop. The program remembers the last state of the input and detects whether the input has changed. If it has, it updates the "last known value" variable and updates the LCD to reflect the change. If you...
  19. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    It is quite possible to make a mistake four times in a row, if it's the same mistake. I understand that you would rather have a single pushbutton for ON/OFF control. I will think about modifying my circuit to have that feature, but not for the next five days - I'll be at my partner's place, and...
  20. KrisBlueNZ

    Bottleneck 555's 0.2A Stuck project

    Chris, I think he doesn't want to buy through ebay.com because of the freight cost. He is obviously on a tight budget. He was considering using ebay.de.
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