This is a continuity tester circuit with a buzzer and LED. Also, I like this circuit. Because unnecessary to take my eyes off the tested circuit. We will hear the buzzer and see LED glows.
Imagine, your circuit does not work, it might be due to solder joint defects. But it is quite hard to pinpoint. Where is the issue occurring? This tester circuit may become useful in this scenario.
The solder joint defects can consist of disconnect in PCB copper, solder bridge, floating lead, lacking solder, etc. Specifically, the increasing rate of human error because of the decrease in the size of electronic components. This problem affects us too.
The main condition of the circuit that we must think about:
- Emit sound and light to get results easily. Expected to use a mechanical buzzer and LED.
- Easy to build, be also an accurate and reliable circuit. Using an integrated circuit(IC) might be a better choice than transistors. We choose IC-741 because of meets the requirements and is cheap, too.
- Low power consumption, can be used with battery for a long time. We will use a 9V battery for this circuit.
Feature of this circuit
We have tested it and found this circuit has the good properties we want.
- Can work when the resistance between two probes is lower than 1Ω.
- Other components connected to the point currently tested, that have a resistance over 1Ω will not affect the testing.
- There is only 200uA and 2mV coming from two testing probes. It definitely does not hurt the circuit we are checking.
- Even if we measure across the semiconductor junctions (P-N), it would not affect the circuit.
Is it better than other continuity testers?
Some tools may damage the devices within the circuit we measure because it outputs current up to 150mA.
How is Continuity tester circuit work
In this circuit below, we use a popular 741 IC as a high gain Op-amp.
The 741 op-amp has many details. If we will learn all of it now, it will cause this post to be too long. For now, we just want to create the circuit. So, we will only look into how to use 741.
See various pins we are using.
- Pin 7: Positive power supply
- Pin 4: Negative power supply
- Pin 6: The output
- Pin 2: The inverting input
- Pin 3: The Non-inverting input
The 741 is good at detecting a tiny amount of voltage.
So, we use it to compare a different voltage between the inverting and Non-inverting input. That difference voltage got increased to be sent to the output. This is called the op-amp comparator.
According to the condition above, we want a probe that can check a resistance under 1 ohm to cause the output to be “high”.
See the circuit, the input section should be a voltage divider with a resistor network. The electric current flows through R1, R2, and R3.
Normally, the voltage across R2 is at some value. But if the resistance across R2 is lower than 1 ohm, the voltage across it is also lower.
Some current comes in the Op-amp’s input through R4. R5.
The output voltage is “high” when the voltage of the non-inverting input is higher than the inverting input.
So, we use R2 to protect the output not to be the negative voltage because the inverting input has a higher voltage than non-inverting.
And, the voltage of non-inverting input can be increased by adjusting the VR1, which will result in the positive voltage at the op-amp’s output.
Connecting buzzer and LED
We can not connect the buzzer and LED to the output directly. Because the output current is too low. And from our experiments, the output voltage is unsuitable for this usage.
The testing process
If the probe receives resistance higher than 1 ohm, the output will be about 1.9V (low state). On the other hand, if resistance is lower than 1ohm, the output will be 6.5V (high state).
We should set the voltage at the “low” state to about 0V and the “high” state to around the power supply voltage (9V).
This issue can be solved by adding to our circuit; 3 diodes connected in series. They will block all of the low state voltage (1.9V) making the low state absolute 0V.
But in the high state, the current can still be passing through to the R7, and Base to Emitter of Q1. Causing Q1 to conduct a larger current from the power supply to power the Buzzer and LED.
How to build and set the circuit
This circuit has quite a few components. So, we can assemble them on the perforated PCB easily.
We are making the prototype of the continuity tester circuit using 741.
Recommended: If you are a beginner, read Electronic components list with images.
How to set and test
Here is a step-by-step quickly setting.
- Take a 1-ohm resistor to test it on the probes.
- Adjust VR1 until the buzzer emits and the LED glows.
- Check it with a 2.2 ohms resistor, the buzzer should have no sound and no light.
- Test it with other PCBs and wires.
0.25W metal/carbon film Resistors, tolerance: 5%
- R1, R3: 22K
- R2: 10Ω
- R4, R5, R8: 1K
- R6: 470K
- R7: 2.2K
- IC1: LM741 or UA741 or HA1741 or Equivalent
- Q1: PN2222 or 2N3904 or S9013
- D1-D3: 1N4148, 75V 150mA, Silicon Diode
- C1: 10uF 16V Electrolytic capacitor
- LED1: 5mm LED, any color
- C1: 10uF 16V Electrolytic capacitor
- BZ1: Mechanical buzzer, 6V-9V
- S1: On-off small slide Switch
- B1: 9V battery with snap battery Or 9V power supply circuit
- PCB, Wires, others
We like this tool because it has high efficiency, and meets the needs. Most importantly, we built it ourselves, cheap! What do you think?
You may also like these circuits
- How to test a diode without meter
- Battery voltage monitor circuit using LM339
- The Op-amp IC tester circuit
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I love electronics. I have learned them by creating the Electronic Circuits and Simple projects to teach my children. Most importantly I hope sharing our experience on this site will be helpful to you.
Hii ni mzunguko wa mtihani wa kuendelea na buzzer na LED. Pia, napenda mzunguko huu. Kwa sababu si lazima kuchukua macho yangu mbali mzunguko majaribio. Tunasikia sauti ya kengele na kuona mwangaza wa LED. Fikiria, mzunguko wako haufanyi kazi, inaweza kuwa kutokana na kasoro za pamoja solder. Lakini ni vigumu sana kuamua ni nini hasa. Tatizo hilo linatokea wapi? Hii circuit tester inaweza kuwa na manufaa katika hali hii. Matatizo ya solder pamoja inaweza kuwa na disconnect katika PCB shaba, solder daraja, kuelea risasi, kukosa solder, na kadhalika. Kwa mfano, kiwango cha makosa ya binadamu kinaongezeka kwa sababu ya kupungua kwa ukubwa wa vipengele vya elektroniki. Tatizo hilo hutufanya sisi pia tuwe na wasiwasi. Hali kuu ya mzunguko kwamba ni lazima kufikiri juu ya: - Emit sauti na mwanga kupata matokeo kwa urahisi. Inatarajiwa kutumia buzzer ya mitambo na LED. - rahisi kujenga, kuwa pia mzunguko sahihi na ya kuaminika. Kutumia mzunguko jumuishi (IC) inaweza kuwa chaguo bora kuliko transistors. IC-741 ni moja ya aina ya IC-741 ambayo ni rahisi na rahisi kutumia. - Matumizi ya chini ya nguvu, inaweza kutumika na betri kwa muda mrefu. Kwa mfano, unaweza kutumia betri ya 9V kwa mzunguko huu. Mzunguko huu umejaribiwa na umegundua kuwa una sifa nzuri ambazo tunataka. - Inaweza kufanya kazi wakati upinzani kati ya vipima mbili ni chini ya 1Ω. - Vipengele vingine kushikamana na hatua kwa sasa majaribio, ambayo kuwa na upinzani zaidi ya 1Ω si kuathiri majaribio. - Kuna tu 200uA na 2mV kuja kutoka probes mbili za kupima. Kwa hakika haidhuru mzunguko tunaoangalia. - Hata kama sisi kupima katika makutano semiconductor (P-N), itakuwa si kuathiri mzunguko. Je, ni bora kuliko vipimaji vingine vya kuendelea? Vifaa vingine vinaweza kuharibu vifaa ndani ya mzunguko tunaopima kwa sababu hutoa mkondo wa hadi 150mA. Mzunguko wa mtihani wa kuendelea (CTC) ni mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo wa mfululizo. 741 Op-amps ni moja ya vifaa vya kuvutia zaidi katika historia. Kama sisi kujifunza yote sasa, itakuwa kusababisha chapisho hili kuwa muda mrefu sana. Kwa sasa, tunataka tu kuunda mzunguko. Kwa hiyo, tutaangalia tu jinsi ya kutumia 741. Angalia pini mbalimbali tunazotumia. Pini 7 - Pini ya nguvu ya nguvu - Pini ya nguvu ya nguvu - Pini ya nguvu ya nguvu - Pini ya nguvu ya nguvu - Pini ya nguvu ya nguvu - Pini ya nguvu ya nguvu - Pini ya nguvu ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu - Pini ya nguvu Hivyo, sisi kutumia yake kulinganisha voltage tofauti kati ya inverting na Non-inverting pembejeo. Hiyo voltage tofauti got kuongezeka kutumwa kwa pato. Hii inaitwa op-amp comparator. Kwa mujibu wa hali hapo juu, tunataka probe ambayo inaweza kuangalia upinzani chini ya 1 ohm kusababisha pato kuwa <unk>high<unk>. Angalia mzunguko, sehemu ya pembejeo inapaswa kuwa divider voltage na mtandao resistor. Mtiririko wa umeme unaingia katika R1, R2 na R3. Kwa kawaida, voltage katika R2 ni katika thamani fulani. Kwa mfano, kama R2 ni chini ya 1 ohm, basi voltage ya R2 ni chini. Baadhi ya sasa inakuja katika Op-amp <unk>s pembejeo kupitia R4. R5 au R5 voltage pato ni <unk>high<unk> wakati voltage ya non-inverting pembejeo ni ya juu kuliko inverting pembejeo. Kwa hiyo, R2 ni muhimu kwa ajili ya kuhifadhi voltage ya nje, kwa sababu inverters ni kubwa kuliko inverters. Na, voltage ya non-inverting pembejeo inaweza kuongezeka kwa kurekebisha VR1, ambayo itasababisha voltage chanya katika op-amp <unk>s pato. Kuunganisha buzzer na LED Hatuwezi kuunganisha buzzer na LED kwa pato moja kwa moja. Kwa sababu pato sasa ni chini sana. Na kutoka majaribio yetu, voltage pato ni haifai kwa ajili ya matumizi haya. Kwa mfano, kama mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani wa mtihani. Kwa upande mwingine, kama upinzani ni chini ya 1 ohm, pato itakuwa 6.5V (kiwango cha juu). "Kama ""kiwango cha chini"" voltage ni 0V, ""kiwango cha juu"" voltage ni 9V." Hii inaweza kuwa na matokeo mazuri kwa kuongeza diodes tatu zilizounganishwa kwa mfululizo. Hii inamaanisha kwamba voltage ya hali ya chini ya 1.9V inaweza kuondolewa na hali ya chini ya 0V. Lakini katika hali ya juu, sasa bado inaweza kuwa kupita kupitia kwa R7 na msingi kwa emitter ya Q1. Kwa mfano, Q1 inaweza kuendesha umeme kutoka kwa umeme wa umeme kwa nguvu ya Buzzer na LED. Jinsi ya kujenga na kuweka mzunguko Mzunguko huu ina vipengele kadhaa. Kwa hiyo, tunaweza kukusanya yao juu ya PCB perforated kwa urahisi. Kwa mfano, unaweza kuunda mzunguko wa mtihani wa kuendelea kwa kutumia 741. Kupendekezwa: Kama wewe ni mwanzoni, kusoma orodha ya vipengele vya elektroniki na picha. Jinsi ya kuweka na mtihani Hapa ni hatua kwa hatua haraka kuweka. - Kuchukua 1-ohm resistor ya mtihani juu ya vipimo. -Kurekebisha VR1 mpaka buzzer emits na LED glows. Kwa mfano, unaweza kutumia kipaza sauti cha 2.2 ohm, lakini kwa kweli, kipaza sauti cha 2.2 ohm haipaswi kuwa na sauti ya sauti. - Jaribu na PCB nyingine na waya. R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W, R: 0.25W. Kwa sababu ya uwezo wake wa kuendesha gari, unaweza kutumia vifaa vya umeme kama vile: Jambo la maana zaidi ni kwamba, tulijenga wenyewe, kwa bei nafuu! Unafikiri ni nini? Unaweza pia kama hizi: Jinsi ya kupima diode bila mita: Mzunguko wa mfuatiliaji wa voltage ya betri kwa kutumia LM339: Mzunguko wa mtihani wa Op-amp IC: Picha zote za ukubwa kamili na PDF za chapisho hili ziko katika kitabu hiki hapa chini. Tafadhali niunge mkono. Ninapenda vifaa vya elektroniki. Nimejifunza kwa kuunda miradi ya Mzunguko wa Elektroniki na Rahisi ya kuwafundisha watoto wangu. Na zaidi ya yote, tunatumaini kwamba kushiriki uzoefu wetu katika tovuti hii itakuwa na manufaa kwa ajili yenu.