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| Brymen IR connection protocol - Anyone sniffed it yet? |
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| t1d:
I have done some testing of the IR componentry, tonight, and I am not getting the results that I expected. Here is some background: I had Jadew explain his IR circuitry to me. Here is his explanation: "Hey Tom, PD6 in that schematic (the RX input) is set to high impedance, so the MCU doesn't have much influence on what happens there. Now, the RX diode is tied to VCC and connected through R4 to ground, that means that the point between the diode and the R4 (on the PD6 input) will be at ground potential when no light shines on the diode, because the LED won't conduct, but the resistor will and it will pull the line to ground. When you shine light on it, it becomes conductive and the diode will try to pull the line to VCC - 0.6V. In order to do that, it has to be able to pull the line harder to VCC than the resistor is pulling it to ground. This means that the resistor has to be high enough to allow the diode to do that easily, but also low enough to be able to quickly pull the line back down when light goes off. I selected it by trial and error. Basically I put my oscilloscope on the PD6 input and changed resistors to see how the waveform changes. If the resistor was too low (it was pulling harder to ground) then the signal was having trouble getting to a high level, if the resistor was too high, then it was having trouble getting to a low level. I think what this means is that 330 seems to be the right value for the diode I used, but it may very well worked for what you have too. For the TX LED, it's about the same, but you have to make sure you don't feed more current to the LED than it can take. Ideally, you want it to be as bright as possible. In my case I fed it more than its rated current (5V / 150 Ohms = .033 mA), but that's up to you. Try with a 330 Ohm resistor first and see how it goes, if it works, then there's no reason to make it lower. Also, check the datasheet of the MCU and see how much current you can source from an I/O." I have laid out a circuit on my breadboard. See jpeg. - R6 and the IR-LED are Jadew's transmit circuitry. I powered it directly from my 5v supply. Jadew drives it off of the chip pin. It makes no difference to the IR-LED from where it gets it supply, so long as it does get proper power. - R5 and the PT are Jadew's receive circuitry. See above, for his description of how the circuit works. The PT is grounded through a 330R resistor. It also feeds the Rx pin on the Controller. I approximate the chip with the resistor/LED indicator light, shown in the gold box. These resistors were random breadboarding parts, with values adding up to more than 200R and less than 1000R. - I am using the QED123 and QSD124 IR components. I don't think these are the parts that Jadew used. My breadboard circuit is intended to switch the indicator LED on and off, by covering the PT. However, this is not the response that I get; the LED illuminates with the PT uncovered, or covered. I will need to back up a step and test the IR components, individually, for functionality. Also, I am not feeling well, tonight, therefore I could have easily missed an obvious circuitry problem, particularly balancing the resistor values (that's above my pay grade,) or wired things incorrectly on the breadboard. Anyway, this is what I have been playing with... |
| t1d:
Here is a little math, for the voltage divider created by Jadew's 330R resistor and my 500R resistor array: Indicator LED Voltage En = Et * (Rn/Rt) En = 5v * (500R/830R) En = 5 * (0.6) En = 3v So, the indicator LED is seeing approximately 3 volts. This is a descent voltage for it... And, purely a happy accident! PT Voltage En = Et * (Rn/Rt) En = 5v * (330R/830R) En = 5 * (0.4) En = 2v This is below the maximum 5v rating. However, I think I have the IR LED/QED123 circuit wired in parallel to the above. So, those numbers need to be considered, but not tonight... Also, the resistances of the IR LED and the PT might should be included... Any insight into what I have wired incorrectly is appreciated. |
| t1d:
--- Quote from: JackM on June 15, 2016, 06:15:14 pm ---Nice progress t1d! I would be interested in getting one of these boards for my own Brymen BM867s if you do find that they work as intended. --- End quote --- Jack, I have sent you a private message. |
| t1d:
I have been thinking on how to create the box to pot the Lockstep components. The method I mentioned, earlier, will work just fine, but I wanted to make it better. So, here are my thoughts... See jpeg. Find a bottle cap that is just smaller than the width of the Lockstep Board. You want the curved locking edges of the board to be outside the diameter of the cap. I am using a cap from a 90 day supply Nexium bottle. Drill a hole in the center of the cap that snugly accommodates the board's wire. Solder up the Lockstep, with its wire and components. Pass the wire through the hole in the cap and seat the components (upside down) inside the cap. Seal the hole, around the wire. Pour in potting fluid. You need to fill the cap with potting fluid, until the fluid is sitting proud of the top of the cap... Bulging above the top of the cap, but not running over. This will make sure that the potting fluid is making contact with the Lockstep board and completely covering the components. Once cured, solder the wire to the controller. This method has several advantages: - The cap creates a proper knob shape that will be easy to twist to lock the board to the DMM. - The cap creates a ready-made "box," in which to pot the components. - Potting with the components pointing downward into the cap/box means that the potting fluid will not seep through the IR component lens holes so easily. But I still recommend sealing the holes, best as you can... Maybe a little toilet paper and white glue? Things to note: - Put a weight on the Lockstep board to hold the components down in the cap, before filling it with potting fluid. - An old coiled cord from a phone handset makes a nice, stretchy wire. It has the needed four conductor wires. However, it does not have a ground shield. |
| Sairus:
Ok plan B, I have not turned the original idea so I did everything from scratch. I made a cable to the microcontroller and wrote a program (Temporarily not possible to build charts but the program itself is quite functional) On further development, I will write here. In the help tab of software is a description how to make your cable. https://www.dropbox.com/s/h4swxm0kkngq294/brymen%20rs.exe?dl=0 |
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