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| university:courses:alm1k:circuits1:alm-measure-outside-0-5-range [27 Jan 2021 22:36] – use wp> interwiki links Robin Getz | university:courses:alm1k:circuits1:alm-measure-outside-0-5-range [05 Sep 2021 22:14] – add off the shelf dividers Doug Mercer |
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| ======Activity: Measuring Voltages Outside 0-5 V Range with ADALM1000====== | ======Measuring Voltages Outside 0-5 V Range with ADALM1000====== |
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| =====Objective:===== | =====Objective:===== |
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| The objective of this document is to provide information and techniques on how to measure voltages outside the native 0-5 V range of the ADALM1000 while performing Active Learning Lab activities. | The objective of this document is to provide information and techniques on how to measure voltages outside the native 0-5 V range of the ADALM1000 (M1k) while performing the Active Learning Lab activities. |
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| =====General Notes:===== | =====General Notes:===== |
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| <WRAP centeralign>Figure 8, R<sub>1</sub> = 1.0 MΩ, R<sub>2</sub> = 200 KΩ, R<sub>3</sub> = 470 KΩ with (orange), without (dark orange) compensation</WRAP> | <WRAP centeralign>Figure 8, R<sub>1</sub> = 1.0 MΩ, R<sub>2</sub> = 200 KΩ, R<sub>3</sub> = 470 KΩ with (orange), without (dark orange) compensation</WRAP> |
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| | ====10X Scope Probes==== |
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| Finally, a common 10X (passive) scope probe can be used. To connect the probe to the Channel B input of the M1K just a BNC connector with short leads terminated in male pins is used. The input end of the probe is connected to the Channel A output to test/calibrate the divider as shown in the photo of figure 9. It is difficult to inject a DC offset when using the probe so the input voltage range will be just positive voltages up to 10X the 0-5 V native range of the M1k or 0 to +50 V. | Finally, a common 10X (passive) scope probe can be used. To connect the probe to the Channel B input of the M1K just a BNC connector with short leads terminated in male pins is used. The input end of the probe is connected to the Channel A output to test/calibrate the divider as shown in the photo of figure 9. It is difficult to inject a DC offset when using the probe so the input voltage range will be just positive voltages up to 10X the 0-5 V native range of the M1k or 0 to +50 V. |
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| With the software frequency compensation feature in ALICE 1.3 and a couple of resistors you can measure just about any range of voltages you need. Obvious first choices would be to use a 1 MΩ for R<sub>1</sub> and either 1 MΩ, 470 KΩ, 200 KΩ or 100 KΩ for R<sub>2</sub>with R<sub>3</sub> left open. It is good practice to keep one or more of these simple voltage dividers installed at one end of your breadboard (to keep it away from any high frequency switching noise from DC-DC power converters or regulators) for use at all times. | With the software frequency compensation feature in ALICE 1.3 and a couple of resistors you can measure just about any range of voltages you need. Obvious first choices would be to use a 1 MΩ for R<sub>1</sub> and either 1 MΩ, 470 KΩ, 200 KΩ or 100 KΩ for R<sub>2</sub>with R<sub>3</sub> left open. It is good practice to keep one or more of these simple voltage dividers installed at one end of your breadboard (to keep it away from any high frequency switching noise from DC-DC power converters or regulators) for use at all times. |
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| | =====Appendix: Off the Shelf Voltage Dividers===== |
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| | The analog inputs on the Arduino microcontroller boards allow 0 to +5V input voltages much like the M1k and require a voltage divider to measure larger voltages. An online search for “Arduino voltage sensor divider” will turn up a number of pre-built resistor voltage divider adapter boards. |
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| | One such board is the [[https://www.digikey.com/en/products/detail/osepp-electronics-ltd/VOLT-01/11198557?utm_adgroup=Development%20Boards%2C%20Kits%2C%20Programmers&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_DK%2BSupplier_Osepp%20Electronics&utm_term=&utm_content=Development%20Boards%2C%20Kits%2C%20Programmers&gclid=Cj0KCQjw1dGJBhD4ARIsANb6OdlkZCgeRSoYZKqV5LGRrLbT0YfXmNkRgO-4G41NY-cwy39Hv0l0oU0aApXIEALw_wcB|VOLT-01]] available from Digikey by OSEPP Electronics LTD. The board and its schematic are shown in figure A1. The 5 to 1 voltage divider is made with 30 KΩ and 7.5 KΩ resistors which gives a total input resistance of 37.5 KΩ. That is much smaller than the M1k built in resistance of 1 MΩ and may load sensitive circuits but probably sufficiently high for measuring power supply voltages up +25V which is its stated purpose. As we can see in the schematic the input screw terminal ground (common) and the output pin header ground (common) are connected together and to the grounded end of the resistor divider (7.5K resistor) which does not allow for inserting a positive offset to allow measuring negative voltages. |
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| | {{ :university:courses:alm1k:circuits1:input-divider-fig-a1.png?600 |}} |
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| | <WRAP centeralign>Figure A1, VOLT-01 5:1 voltage divider board</WRAP> |
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| | Another simple divider board, the DFR0051, is available through [[https://www.arrow.com/en/products/dfr0051/dfrobot| Arrow]] and [[https://www.digikey.com/en/products/detail/dfrobot/DFR0051/6579310?s=N4IgTCBcDaICIDEBKAGFBWAjCAugXyA|Digikey]] and [[https://www.newark.com/dfrobot/dfr0051/analogue-voltage-divider-v2-arduino/dp/87AH5865|Newark]]. |
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| | This also appears to be a 5:1 divider with the same 30 KΩ and 7.5 KΩ resistors and common input and output ground terminals but with the addition of an LED and 470 Ω series resistor connected across the input voltage terminals. The 470 Ω resistor seems a little small based on 25 V Max on the input, the LED current would be around 50 mA which would burn out most SMD LEDS. Also not something you would necessarily want across the thing you measuring. But once the LED burns out and becomes an open circuit that issue goes away. |
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| | {{ :university:courses:alm1k:circuits1:input-divider-fig-a2.png?600 |}} |
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| | <WRAP centeralign>Figure A2, DFR0051 5:1 voltage divider board</WRAP> |
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| | This third option, the 36209-MP, available at [[https://www.mpja.com/Voltage-Divider-Module-for-Arduino/productinfo/36209%20MP/ | MPJA.com]] has a divider ratio of 0.18 (~5.55X) using 820 KΩ and 180 KΩ resistors. The 1 MΩ total input resistance is much better than the other two examples and close to the M1k’s built-in 1 MΩ. However, it too has the grounds terminals (commons) connected together and to the grounded end of the resistor divider (180K resistor) which does not allow for inserting a positive offset to allow measuring negative voltages. |
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| | {{ :university:courses:alm1k:circuits1:input-divider-fig-a3.png?600 |}} |
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| | <WRAP centeralign>Figure A3, 36209-MP 5.55:1 voltage divider board</WRAP> |
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| **For Further Reading:** | **For Further Reading:** |
